Twenty Years of Research on Millennials at Work: A Structural Review Using Bibliometric and Content Analysis

Abstract

This study reviews the literature regarding millennials at work over the past 20 years (from 2000 to 2020). Bibliometric methods of citation, co-citation and bibliographic coupling analysis, as well as traditional content analyses, were performed on a sample of 377 articles retrieved from ISI Web of Science (WOS). Citation analysis revealed influential articles, authors, journals and countries. Co-citation analysis and bibliographic coupling identified six historic research streams and four current research fronts. The content analysis finally led to the identification of the future research questions. The study explores the body of literature on millennials at work over the last 20 years and offers context and placement in the literature for prior studies by presenting the historical and current state of research. Further, recommended research questions are identified for future research. Finally, we present implications for HRM practice and research.

1. Introduction

Research on generations has been around for some time. Mannheim’s [1] seminal work in this area suggests that generations contain two essential components: a common location in a historic time period and a distinct consciousness that is the result of important events of that time. Mannheim’s work predates but is reflected in, commonly used conceptualizations of generations based on age, such as baby boomers, Generation X, etc. These conceptualizations have their roots in the generational cohort theory, developed by Inglehart [2] and later made popular by Strauss et al. [3]. Strauss, Strauss and Howe [3] defined a generation as: “a special cohort-group whose length approximately matches that of a basic phase of life, or about twenty-two years’’ (p. 34). Later, Kupperschmidt [4] added a developmental and cultural aspect to the definition: “an identifiable group that shares birth years, age, location, and significant life events at critical developmental stages’’ (p. 66). The principle behind the concept of generations is that individuals are influenced by historical events and cultural phenomena that occur during key developmental stages typically late childhood, adolescence, and early adulthood [5]. While there is general consistency across generations’ conceptualizations on birth years, development and culture, there is substantial variance in exactly when each generation starts and ends. For example, the baby Boom generation, about which there seems to be the most agreement on start and end dates, has starting years ranging from 1943 to 1946 and ending years from 1960 to 1969. Generation X has starting years varying from 1961 to 1965 and continuing on to 1975 to 1981 [5]. There is a similar pattern for the millennial generation or Gen Y.

Therefore, in the same vein, the millennial generation, or Generation Y, can be defined as individuals born during the last two decades of the twentieth century [5,6]. Since the popular press recognizes millennials as an emerging generational group in today’s global workforce, executives, policymakers and academics have committed ample resources to understand them at work [7]. As a result, the last two decades have seen a rapid increase in the number of research articles exploring the millennial generation at work. Former research mostly studied the previously predominant generations in the workplace i.e., baby boomers and Generation X [4,8]. Research on millennials at work dates from the beginning of the 2000s, though interpretation of the generation had begun earlier [9]. In 2000, when the eldest of the millennials were about 20, a seminal book by Howe and Strauss [10] described the millennial generation as special, vital, full of promise, sheltered, confident, team-oriented, achieving, pressured and conventional. The same year a book by Zemke et al. [11] focused on managing and working with people from different generational groups (veterans, boomers, Generation Xers and nexters/millennials). Two years later, Lancaster and Stillman [12] talked about the similarities and variations between different generations in the workplace, and [13] explored the differences in work values between different generations at work (WWIIers, swingers, baby boomers, Generation Xers and millennials).

Since 2002, various empirical research studies to further understand millennials at work have reported contradictory findings [14]. For example, work from Twenge [15,16,17] identified millennials as narcissistic and with less concern for others, and hence labelled them as Generation Me. Whereas other studies found millennials to have more of a sense of morality/ethics than previous generations [18,19]. Another debate surrounding millennials surrounds the question as to whether they are the first global generation. There is inadequate empirical evidence to prove or disprove the assertion that millennials are the first global generation [20], with a generational consciousness that transcends national culture. Further, scholarship has yet to fully understand if millennials at a later stage in their career differ from those earlier in their careers [21] and/or if millennials are a homogenous or heterogeneous group [22]. Finally, while more recent and extensive media coverage, social media attention and popular culture references have made the term millennial a social meme [23], academic research has become increasingly critical of generational labelling [24,25,26,27,28,29]. Therefore, to understand these debates, our bibliometric review examines the body of literature over the last 20 years, including how research studies on millennials at work relate to or build on each other. Further, various review studies and theoretical articles have been written to explore generations and generational differences [30,31,32]. Other reviews have studied values, attitudes and behaviours of millennials in the workplace [33,34,35,36]. While these studies carried out extensive reviews of past literature on millennials at work, most of the review work was done almost a decade ago and, given the recent growth of literature on the subject, does not include the latest research trends. For this reason, we see the present need for another review paper to present the existing work and show how research has evolved and shaped other research on millennials at work over the past 20 years. We believe now is an important time to review the literature because the eldest millennials are now 38–40 years old and have entered key positions in organizations [37]. In our review paper, we utilize bibliometric methods of citation, co-citation and bibliographic coupling analysis (utilizing VOSviewer and HistCite), as well as traditional content analysis. The methodology of our review differs from prior review studies, which have adopted more traditional review methods and which are susceptible to review authors’ specialization-in-the-field bias [38,39].

To fill in the gap in research on millennials at work, we used the following research questions to examine how millennials at work articles have evolved in the past 20 years:

(RQ1) Which mediums (articles, authors, journals, institutions and countries) are the most influential in the research on millennials at work?

(RQ2) What historic research streams emerge within the literature on millennials at work?

(RQ3) What are the (a) current research fronts and (b) future research questions?

Our study contributes to the literature on millennials at work in several ways. First, our citation analysis of the literature on millennials at work identifies key authors, articles, journals, institutions and countries to be considered for future research on the topic. Second, our co-citation analysis and bibliographic coupling, coupled with content analysis, extend earlier reviews by identifying the core structure of research on the topic in the past 20 years, identifying the underlying historic research streams, the current research fronts, a profile of millennials (categorized in terms of work, personal and psychological values, traits and attitudes) and future research questions. Finally, we present implications for HRM practice and research. This X-ray of research may help researchers and practitioners to circumnavigate the different avenues for their future research and help them in identifying possible ideas and interventions that deserve more attention. The remainder of the paper is organized as follows: Section 2 describes bibliometric techniques and their suitability for our study, Section 3 describes our data search and analysis strategy, Section 4 presents the results, Section 5 provides discussion and implications, and Section 6 discusses the limitations of the study and concludes.

2. Bibliometric Analysis

In recent years, bibliometric techniques have been utilized to effectively analyse scientific literature and reveal insightful details such as the structure of academic collaboration networks [40,41] and citations, co-citations, bibliographic coupling and keyword co-occurrence [38,42,43,44].

Software such as HistCite and VOSviewer has been used to implement bibliometric techniques. HistCite performs citation analysis of the WOS database by providing the most important articles, authors, institutions and countries in terms of various metrics such as total local citations (TLC), the number of times a retrieved article is cited by others within the retrieved set of articles; total global citations (TGC), the number of times a retrieved publication is cited in the WOS database; average local and global citations per year (TLC/t, TGC/t); and the local citation score at the end (LCSe), local citations at the end of the time period, to name a just a small number (refer to Appendix B for metrics and their abbreviation).

Moreover, HistCite also builds a co-citation graph based on either local or global citations. The graph further helps to identify underlying research streams by analysing the content of the most cited articles. VOSviewer provides co-authorship, co-occurrence of keywords, citations, bibliographic coupling and co-citation analysis. Prior research has utilized one or both of these software packages to perform citation, co-citation, keyword co-occurrence and bibliographic coupling analysis of literature on consumer–brand relationships [43]; absorptive capacity [42,45]; green supply chain management [44]; public leadership [46]; and expatriate research [38] to reveal the historic and current structure of research, influential channels and future research directions. Our study focuses on the historic and current structure of research on millennials at work, the research streams that emerge and the influential mediums for which bibliometric techniques are suitable.

3. Methods

On 30 December 2020, we searched the WOS database for publications over the period 2000–2020 with the term Millennial*, generation y*, and gen y* in their title or topic. The WOS database was preferred over other databases, such as Google Scholar or Scopus, because many notable bibliometric reviews have used this database before [42,43,44,46,47]. Further, recent reviews comparing different publication databases show that WOS has the top-tier quality of publications, is designed for citation analysis, and is thus compatible with most citation analysis tools [48]. The year 2000 was chosen as a benchmark year because millennials may have been nearing entry into the workforce [33]. Additionally, as indicated in the introduction in the year 2000, two seminal books on millennials were published. The initial search revealed 15,037 records which were refined further by WOS categories (Psychology Multidisciplinary OR Business OR Management OR Psychology Social OR Public Administration OR Psychology Applied OR Business Finance), resulting in 1542 relevant publications. These categories were chosen because of the organizational focus of our research. We only included articles and review articles, written in English.

The records were then downloaded and imported into the VOSviewer to collect the keywords of these 1542 articles (all keywords with five or more occurrences) to assess the content of the research on millennials [45]. VOSviewer can classify those keywords into different clusters: those located near each other depict high co-occurrence in articles, and those further apart demonstrate low co-occurrence. Each keyword cluster represents a research stream on millennials [42]. We identified two distinct research clusters: millennials as consumers, and millennials at work.

Our focus was on the latter, millennials at work, stream of research. Therefore, we further refined our WOS search with the frequently co-occurring keywords identified from the keyword co-occurrence analysis (within the millennials at work cluster). The keywords were: cohort*, generational difference*, work*, value*, work value*, workplace*, attitudes*, performance*, behavior*, satisfaction*, commitment*, motivation*, career*, psychological contract*, turnover*, leadership*, recruitment*, age*, personality*, business ethic*, corporate social responsibility*, ethic*, and sustainability*. The search yielded 305 records. The records were then imported again in VOS viewer to perform a co-citation analysis with cited references as our unit of analysis. The purpose was to also include external WOS references that shared a high number of co-citations with our sample articles (five or more citations), in our final sample [49]. The procedure resulted in an additional 72 articles and so we reached a final sample of 377 articles on millennials at work. Figure 1 depicts a flow diagram of the search strategy.

The 377 records were then imported into HistCite for further analysis of influential mediums (authors, articles, journals, institutions, and countries) to address RQ1. In order to answer RQ2, we first used HistCite to visualize the co-citation/historiographic map based on TLC (number of times a paper is cited by others within our retrieved set of 377 papers). To get an interpretable co-citation map, we only considered the articles cited ten or more times locally (TLC ≥ 10). Previous studies have used similar limits to show the most important citation links within the collection, simultaneously maintaining both the good readability of the graph and an understanding of the research streams emerging from the most important articles [42,50]. Co-citation/historiographic maps depict how articles are co-cited reciprocally over time (relationship between cited documents) and helps in identifying the historic core, or skeleton, of research [43,50]. To answer RQ3(a), we performed bibliographic coupling of articles published from 2015 to 2020. Bibliographic coupling reveals the network of citing documents and helps in identifying the current research fronts because it traces more recent publications, independently of the frequency with which they have been cited [38,46].

We analysed the content of the articles using a concept matrix developed in MS Excel [44,51]. This matrix consists of node id, authors, article title, publication year, journal, data and sample, context, methodology, theory, type of study, key findings and recommendations for future research columns. Using content analysis of latest and top-journal articles we answered RQ3(b) by obtaining the future research questions from articles’ recommendations for future research.

4. Results

Figure 2 presents the number of articles published (P_MAW), TLC and TGC, using line and bar graphs, respectively. The line graph shows there were fluctuations in the number of articles published between 2000 and 2014, with significant peaks in P_MAW, TLC and TGC observed in the years 2008 and 2010. From 2014 to 2019, however, there was a sharp rise in the number of publications, with 219 (58%) of the 377 articles published during that period.

4.1. Most Influential Articles and Trending Papers

To address part of RQ1,

Table 1. Rank of top 10 articles (sorted by total global citations per year—TGC/t).

Rank	Author/Year/Title/Journal	TLC	TLC/t	TGC	TGC/t
1	Twenge et al. (2010) [52]. Generational Differences in Work Values: Leisure and Extrinsic Values Increasing, Social and Intrinsic Values Decreasing. Journal of Management	61	5.55	415	37.73
2	Smola and Sutton (2002) [13]. Generational differences: revisiting generational work values for the new millennium. Journal of Organizational Behavior	74	3.89	542	28.53
3	Lyons and Kuron (2014) [32]. Generational differences in the workplace: A review of the evidence and directions for future research. Journal of Organizational Behavior	30	4.29	185	26.43
4	Parry and Urwin (2011) [31]. Generational Differences in Work Values: A Review of Theory and Evidence. International Journal of Management Reviews	45	4.50	244	24.40
5	Cennamo and Gardner (2008) [53]. Generational differences in work values, outcomes and person-organisation values fit. Journal of Managerial Psychology	49	3.77	305	23.46
6	Ng et al. (2010) [54]. New Generation, Great Expectations: A Field Study of the Millennial Generation. Journal of Business and Psychology	49	4.45	250	22.73
7	Twenge et al. (2012) [17]. Generational Differences in Young Adults’ Life Goals, Concern for Others, and Civic Orientation, 1966–2009. Journal of Personality and Social Psychology	17	1.89	200	22.22
8	Twenge and Campbell (2008) [55]. Generational differences in psychological traits and their impact on the workplace. Journal of Managerial Psychology	47	3.62	233	17.92
9	Myers and Sadaghiani (2010) [34]. Millennials in the Workplace: A Communication Perspective on Millennials’ Organizational Relationships and Performance. Journal of Business and Psychology	35	3.18	186	16.91
10	Gursoy et al. (2008) [56]. Generational differences: An examination of work values and generational gaps in the hospitality workforce. International Journal of Hospitality Management	24	1.85	214	16.46

presents the TLC, TLC/t, TGC, and TGC/t of the top 10 articles. The articles were ranked (in descending order) by TGC/t and all can be considered highly influential in shaping research on millennials at work. Table 1 shows that the most highly cited articles were published from 2002 to 2012. Most of the articles are on intergenerational differences.

Next, we examined trending articles to identify not only the origin of the research on millennials at work but also to where it is heading.

Table 2. Rank of top 20 trending articles (sorted by LCSe).

Rank	Author/Year/Title/Journal	LCSe	TLC/t	TGC/t
1	Ng et al. (2010) [54]. New Generation, Great Expectations: A Field Study of the Millennial Generation. Journal of Business and Psychology	24	4.45	22.73
2	Parry and Urwin (2011) [31]. Generational Differences in Work Values: A Review of Theory and Evidence. International Journal of Management Reviews	21	4.50	24.40
3	Twenge et al. (2010) [52]. Generational Differences in Work Values: Leisure and Extrinsic Values Increasing, Social and Intrinsic Values Decreasing. Journal of Management	19	5.55	37.73
4	Lyons and Kuron (2014) [32]. Generational differences in the workplace: A review of the evidence and directions for future research. Journal of Organizational Behavior	17	4.29	26.43
5	Hershatter and Epstein (2010) [33]. Millennials and the World of Work: An Organization and Management Perspective. Journal of Business and Psychology	16	2.91	15.09
6	Twenge and Campbell (2008) [55]. Generational differences in psychological traits and their impact on the workplace. Journal of Managerial Psychology	15	3.62	17.92
7	Deal et al. (2010) [14]. Millennials at Work: What We Know and What We Need to Do (If Anything). Journal of Business and Psychology	15	3.36	15.36
8	Smola and Sutton (2002) [13]. Generational differences: revisiting generational work values for the new millennium. Journal of Organizational Behavior	14	3.89	28.53
9	Myers and Sadaghiani (2010) [34]. Millennials in the Workplace: A Communication Perspective on Millennials’ Organizational Relationships and Performance. Journal of Business and Psychology	13	3.18	16.91
10	Cennamo and Gardner (2008) [53]. Generational differences in work values, outcomes and person-organisation values fit. Journal of Managerial Psychology	12	3.77	23.46
11	Costanza and Finkelstein (2015) Generationally Based Differences in the Workplace: Is There a There There? Industrial and Organizational Psychology-Perspectives on Science and Practice	12	2.83	12.00
12	Costanza et al. (2012) [28]. Generational Differences in Work-Related Attitudes: A Meta-analysis. Journal of Business and Psychology	11	3.11	15.56
13	Kowske et al. (2010) [57]. Millennials’ (Lack of) Attitude Problem: An Empirical Examination of Generational Effects on Work Attitudes. Journal of Business and Psychology	10	2.45	10.64
14	Cogin (2012) [58]. Are generational differences in work values fact or fiction? Multi-country evidence and implications. International Journal of Human Resource Management	10	2.11	11.33
15	Wong et al. (2008) [59]. Generational differences in personality and motivation Do they exist and what are the implications for the workplace? Journal of Managerial Psychology	9	2.38	13.08
16	Gursoy et al. (2008) [56]. Generational differences: An examination of work values and generational gaps in the hospitality workforce. International Journal of Hospitality Management	9	1.85	16.46
17	Becton et al. (2014) [60]. Generational differences in workplace behavior. Journal of Applied Social Psychology	8	1.86	7.00
18	Joshi et al. (2010) [61]. Unpacking Generational Identities in Organizations. Academy of Management Review	8	1.82	9.91
19	Hansen and Leuty (2012) [62]. Work Values Across Generations. Journal of Career Assessment	7	1.44	6.33
20	Dries et al. (2008) [63]. Exploring four generations’ beliefs about career Is “satisfied” the new “successful”? Journal of Managerial Psychology	6	1.77	10.92

presents the most influential articles ranked (in descending order) by LCSe. This metric identifies papers cited over a fixed time period and, more recently, allows us to identify emerging topics [42,43]. Table 2 shows that the most highly cited articles were published from 2002 to 2015. Table 1 and Table 2 also identify the most influential authors. (A detailed table of influential authors ranked by P_MAW and citation metrics is available on request.)

4.2. Most Influential Journals

To address the other part of RQ1,

Table 3. Rank of top 10 journals (sorted by P_MAW (left) and TLC/t (right)).

Rank	Journal	PMAW	TLC/t	Journal	TLC/t	PMAW
1	JBP	13	23.11	JBP	23.11	13
2	JMP	10	13.33	JMP	13.33	10
3	ER	8	0.83	JOB	8.82	4
4	CDI	7	3.61	JOM	5.55	1
5	JLS	7	0.20	IJMR	4.50	1
6	JSP	7	0.40	CDI	3.89	7
7	PRR	6	0.27	IJHRM	2.88	4
8	JBE	5	2.31	IJHM	2.88	2
9	SBP	5	0.17	IOP	2.83	1
10	WAR	5	1.75	JBE	2.31	5

shows the top 10 journals that have published research on millennials at work. (See Appendix A for full journal names). Journals are ranked in terms of P_MAW and TLC/t. Of these, the Journal of Business and Psychology (JBP) and Journal of Managerial Psychology (JMP) are the top two journals, both in terms of P_MAW and TLC/t.

To confirm our observations, we mapped the top 10 journals (sorted by TLC/t) in to four quadrants. Figure 3 shows that only two journals, JBP and JMP, lie in the first quadrant (high P_MAW and high TLC/t) whereas the rest of the journals lie in the third quadrant (low P_MAW and low TLC/t). Career Development International (CDI) lies on the boundary of the third and fourth quadrants and can be considered to lie in the fourth (high P_MAW and low TLC/t).

4.3. Most Influential Institutions and Countries

Finally, to answer RQ1, we analysed institutions and their ranks in terms of P_MAW and TGC. We found that the top 10 institutions were located in the United States (U.S.) and Canada. To obtain a complete picture, we then ranked the countrywide research output according to P_MAW and TGC.

Table 4. Rank of top 10 countries (sorted by P_MAW (left) and TGC (right)).

Rank	Country	PMAW	TLC	TGC	Country	PMAW	TLC	TGC
1	U.S.	189	737	6008	U.S.	189	737	6008
2	Canada	27	149	1437	Canada	27	149	1437
3	India	16	7	41	UK	10	92	592
4	Australia	14	69	526	Australia	14	69	526
5	China	11	3	31	Belgium	4	22	339
6	UK	10	92	592	New Zealand	1	48	305
7	Spain	10	2	28	Netherlands	4	11	97
8	South Africa	6	0	4	Germany	4	8	71
9	Belgium	4	22	339	India	16	7	41
10	Netherlands	4	11	97	Croatia	2	5	40

depicts the results and reveals U.S. and Canada as the top two countries, both in terms of P_MAW and TGC, with the U.S. well out in front. Australia is fourth in terms of both P_MAW and TGC, India is third in terms of P_MAW, and the United Kingdom (UK) is third in terms of TGC.

4.4. Co-Citation Mapping

Filtering the locally cited articles 10 or more times (TLC ≥ 10) resulted in 30 articles out of 377 retrieved papers (9.4% of the total retrieved work). Figure 4 depicts the co-citation map of research on millennials at work, with nodes representing articles and lines representing the directed citation ties. The size of the node represents the number of local citations received by the article—the bigger the node size, the more local citations an article has received. The direction of the arrow represents the direction of the citation tie—the paper from which the arrow originates cites the paper the arrow points to. The vertical axis represents the year of publication and the numbers in the nodes represent specific articles in the collection and sort the main bibliography in ascending order by year [50]. After an iterative analysis of the contents of the 30 articles, we identified six distinct but interrelated research streams (RQ2—Figure 4):

• Intergenerational differences: Work values and attitudes
• Intergenerational differences: Psychological traits
• Intergenerational differences: Personal values
• Generational differences: Cross-country evidence
• Intragenerational differences: Millennials
• The Millennial generation

4.4.1. Stream 1: Intergenerational Differences: Work Values and Attitudes

This research stream emerged as the strongest in terms of the number of core publications on millennials at work. The main question it explores is: “Are there generational similarities and/or variations in work values, traits and attitudes among different generations in the workplace?” This stream contains the seminal article by Smola and Sutton [13] (node 6, Figure 4), which found significant differences between boomers and Generation Xers in desirable work outcomes and the moral importance of work. The study addressed millennials from an implication perspective because, in 2002, they were just beginning to enter the workforce. The findings of the rest of the influential articles in this stream report differences in various work values, traits and attitudes (e.g., teamwork, status, freedom, intrinsic and extrinsic values, job satisfaction and mobility, etc.) among generations [18,52,53,56,57,60,62,64] and are reflected in nodes 21, 14, 46, 44, 40, 56, 53, and 85. Notably, the other articles in the stream are review studies that review and critique prior research on intergenerational differences [5,14,28,31] and are reflected in nodes 34, 49, 64, and 107.

4.4.2. Stream 2: Intergenerational Differences: Psychological Traits

The second stream that emerges in the literature explores intergenerational similarities and/or variations in psychological traits. Twenge et al. [55] (node 12, Figure 4) found that, compared with boomers, millennials scored higher on self-esteem, narcissism, anxiety, depression and external locus of control, and lower on need for social approval. Similarly, other articles report differences in personality and motivational traits among generations [59,63], these are reflected in nodes 13 and 15.

4.4.3. Stream 3: Intergenerational Differences: Personal Values

This stream explores intergenerational similarities and/or variations in personal values. Trzesniewski and Donnellan [65] (node 29, Figure 4) found little difference in millennials’ personal values (e.g., self-enhancement, life satisfaction, happiness, importance of religion and social status) as compared with older generations. Twenge, Campbell and Freeman [17] (node 61, Figure 4) on the other hand, found a decline among millennials in personal values such as empathy for outgroups, charity donations, importance of job contributing towards society, interest in social problems, taking action to save environment and energy as compared with older generations, with some of the largest declines occurring in the value related to taking action to save the environment.

4.4.4. Stream 4: Generational Differences: Cross-Country Evidence

This stream provides evidence of generational differences across different countries. Egri and Ralston [66] (node 8, Figure 4) investigated the generational differences in value orientation of Chinese and U.S. managers and professionals and found that the personal values of recent generations differ more than those of earlier generations. Cogin [58] (node 54, Figure 4), using data collected from employees in the American, Australian, Chinese, Singaporean, and German offices of a multinational company, found similarities between countries in generational work values, with Generation Y placing the highest importance on leisure and asceticism compared with other generations across all researched countries.

4.4.5. Stream 5: Intragenerational Differences: Millennials

The next stream explores similarities and differences within the millennial generation and contains only one core article. Ng, et al. [54] (node 41, Figure 4) explored demographic similarities and differences in career expectations and priorities of millennial students from Canada and found that their expectations varied by gender, grade point average (GPA), visible minority status, and year of study.

4.4.6. Stream 6: Generational Theory

The last stream to emerge was the theory-centred stream. All the key articles were scholarly views/reviews discussing the factors influencing and defining the millennials generally [35,67], reflected in nodes 4 and 5 and in organizations [34,36] nodes 9 and 36.

4.5. Bibliographic Coupling

Bibliographic coupling of articles published from 2015 to 2020 reveals a network of 60 citing documents. Figure 5 shows the bibliographic coupling graph. Using clustering techniques and analysis of the content of the 60 articles, we identified four distinct but interrelated current research fronts (RQ3(a)—Figure 5):

• Millennials and ethics
• Millennials at the workplace
• Millennials: HR perspective
• Generations: Critical perspective

4.5.1. Research Front 1: Millennials and Ethics

The first research front explores the ethical profile of millennials. For example, the latest articles have studied millennials’ social values, entitlement, narcissism and uncivil behaviours [68]; personal value orientations, ethical decision making and conscience, ethical judgment and intentions, moral reasoning and awareness and preference for ethical leadership [7,19,22,69,70,71,72]; religion and spirituality [73]; and attitude towards environmental sustainability [74].

4.5.2. Research Front 2: Millennials and Organizational Behaviour

The next research front studies millennials’ workplace behaviour. For example, the latest articles have explored the antecedents of millennials’ affective commitment [75]; job embeddedness [76], turnover (intentions) [77,78], and work motivation [79].

4.5.3. Research Front 3: Millennials: HR Perspectives

The third research front looks at millennials through the HR lens. For example, the latest articles have explored potential employer attractiveness factors such as CSR [80,81], work-life benefits and compensation [82], and legitimacy management [83] for millennial job seekers. Further, there have been articles on recruitment, development and retention of millennial employees [84,85,86]; managing and leading millennials [72,87,88,89,90,91]; millennials work values [21,92]; and millennials as managers/leaders [93].

4.5.4. Research Front 4: Generations: Critical Perspectives

The final research front to emerge is the generation critical front. Latest papers have adopted a critical stance towards the concept of generations. For example, the latest articles report that the age-based cut-offs to determine generations are arbitrary and also differ substantially across cultures; that cross-sectional studies that confound age, period, and cohort effects (which cannot be empirically disentangled) are not adequate; that generations research also commits an ecological fallacy, because it assumes that differences between generational groups apply to (all) individual members of these groups and that this can contribute to age-based stereotyping in organizations by assuming that arbitrarily-formed age groups possess the same psychological characteristics, such as loyalty, entitlement, etc. [24,25,26,27,28,29]. However, a complete abandonment of generational research may not yet be likely, and there are ways forward [94].

4.6. Recommendations for Future Research

Finally, to answer RQ3(b), first, we present a synthesis of millennial values, traits and attitudes obtained from top-journal articles (in terms of TLCs) and more recent articles published in influential journals.

Table 5. Millennials‘ values, traits and attitudes.

Millennials’ Profile	References	Country (Sample)
Work values, traits and attitudes
− Organizational commitment − Job/organizational mobility − Compliance − Turnover intentions − Work engagement − Pro-union attitude − Tech Savvy	(Becton et al., 2014) [60], (Cennamo & Gardner 2008) [53], (Choi et al., 2020) [95], (Glazer et al., 2019) [96], (Kowske et al., 2010) [57], (Lub et al., 2012) [64], (Lyons et al., 2015b) [97], (Hisel 2020) [98], (Smith and Duxbury 2019) [99], (Majer 2020) [89]	U.S. (job applicants), New Zealand (employees-diverse), South Korea (employee-social enterpises), Mixed (employees), U.S. (employees-diverse), Netherlands (employees-hotels), Canada (employees-diverse), U.S. (nurses), U.S. (union members), Central and eastern Europe (employees-Ad agencies)
− Person-organization fit − Extrinsic values − Intrinsic values − Work centrality − Hard work − Protestant work ethic (PWE) − Delay of gratification − Status and freedom values − Social values − Altruistic values − Leisure values − Work-family conflict − Family centrality − Morality/ethics	(Bennett et al., 2017) [100] (Campbell et al., 2017) [101], (Cennamo and Gardner 2008) [53], (Chen and Lian 2015) [102], (Gursoy et al., 2013) [103], (Meriac et al., 2010) [18], (Real et al., 2010) [104], (Smith et al., 2018), (Twenge et al., 2010) [52], (Twenge and Donnelly 2016) [105], (Yang et al., 2018), (Cogin 2012) [58] (Papavasileiou and Lyons 2014) [92], (Boyd 2009) [106], (Yildiz & Yakut 2019) [107], (Weber 2015) [19]	Mixed (employees), U.S. (high school seniors), New Zealand (employees-diverse), China (employees-diverse), U.S. (hotels), U.S. (students), U.S. (employees-construction), Canada (employees-public sector), U.S. (high school seniors), U.S. (students-college), China (employees-diverse), U.S. /Australia/China/Singapore/Germany (employee-multinational), Greece (students-undrgrad), U.S. (students-grad and undergrad), Turkey (employees-diverse), U.S. (students-grad)
− Preferences for: − Collective action and teamwork − Trust in central authority − Optimism of the future − Rotation through projects and roles − Continuous learning and feedback − Paid time off − Compensation − Career progression − Location − Role and work culture − Social relations − Flexible working hours − Good work-life balance − Sustainable and psychologically healthy workplaces	(Gursoy et al. 2008) [56], (Rosa and Hastings 2018) [91], (Madan and Madan 2019) [108], (Ng and Gossett 2013) [109], (Zaharee et al., 2018) [85], (Alonso-Almeida and Llach 2019) [110], (Catano and Morrow Hines 2016) [111], (Waples and Brachle 2019) [81]	U.S. (employees and managers-hotels/hospitality), India (students-under grad and postgrad), Canada (students-universitry), U.S. (employees-IRI member organizations), Spain/Bolivia/ Costa Rica/Argentina/Colombia/ Paraguay (20–30 year olds), Canada (job applicants), U.S. (hypothetical job applicants)
Personal values, traits and attitudes
− Self-focus − Other-focus − Importance of job contributing towards society − Interest in social problems − Taking action to save environment and energy − Empathy for out-groups − Charity donations − Cognitive moral reasoning − Ethical frames of reference	(Twenge et al., 2012) [17], (Weber 2015) [19], (Weber and Elm 2018) [69], (Culiberg and Mihelič 2016) [70]	U.S. (students-highschool/grad/business), Slovenia (students-business)
− Self-enhancement − Life satisfaction − Happiness − Importance of social status − Importance of religion/religiosity 57. Self-transcendence − Spirituality − Asceticism − Openness to change − Conservation	(Lyons et al., 2007) [112], (McMurray and Simmers 2019) [113], (Trzesniewski and Donnellan 2010) [65], (Cogin 2012) [58]	Canada (knowledge workers, students-undergrad business), North America and Asia (employee-diverse), U.S. (students-high school), U.S. /Australia/China/Singapore/Germany (employee-multinational)
Psychological traits
− Self-esteem − Narcissism − External locus of control − Anxiety − Depression − Psychological empowerment − Psychological flexibility	(Twenge et al., 2008) [55], (Twenge et al., 2008b) [15], (Twenge 2009) [16], (Twenge and Foster 2010) [15], (Trzesniewski et al., 2008) [114], (Trzesniewski & Donnellan 2010) [65], (Sobrino-De Toro et al., 2019) [115]	U.S. (students-high school), Spain (employees-diverse)

presents a profile of millennials (categorized in terms of work, personal and psychological values, traits and attitudes). As can be seen from the table, samples are heterogeneous, ranging from high school students to employees in various industries such as hospitality, building trades and public service. In addition, studies have been carried out in various time frames (published as early as 2007 and as late as 2019). Further, while most of the studies are conducted in the U.S., at least 18 different countries are identified in the table. The information in the table can provide material for future research willing to explore whether millennials’ work, personal and psychological values, traits and attitudes change with time and/or country and/or context and/or diverse samples (e.g., industry or student). For instance, researchers studying the young generation in their respective countries can organize the results in Table 5 according to a cultural clustering framework and analyse them using meta-analysis or smallest space analysis to test whether their respective findings support the notion of a global youth generation [92]. Table 5 also seeks to provide researchers with quick access to information on key variables and constructs relevant to their future research and help them to identify additional contributions within the emerging research fronts. For example, future research may consider how key constructs of interest (e.g., expectations) may shift across early careers to later careers for millennials [21].

Second, we obtained specific future research questions from a content analysis of the latest journal articles’ recommendations for future research. The questions were slightly modified to fit the current research front framework.

Table 6. Future research questions.

No.	Research Front	Future Research Questions	References
1.	Millennials and ethics	Are there similarities/differences (e.g. regional, national, institutional, and/or demographic) in personal value orientation and ethics among Millennials?	(Weber and Urick 2017) [22] Culiberg (2016) [70]
		What is a complete description of Millennials’ ethical profile (different and varied ethical issues or scenarios, religion and spirituality)?	(Nelson et al., 2016) [73]
		Are Millennial employees less likely (more likely) to look to ethical leaders for guidance in ethical decision making and to respond to ethical appeals to do right by the organization and its stakeholders?	Anderson (2017) [72]
		Can organizational socialization increase Millennials’ moral awareness?
2.	Millennials at the workplace	What are the antecedents of Millennials’ workplace behavior?	(e.g. Naim and Lenka 2017 [75], Tews et al., 2015 [76], Gulyani and Bhatnagar 2017) [116]
3.	Millennials: HR perspective	Does work-life balance lead to Millennial job seekers’ attraction to organizations?	(Firfiray and Mayo 2017) [82]
		Does economic slowdown (for e.g., in the current COVID-era) affect Millennials’ job decision processes?
		How do firms establish legitimacy in the eyes of prospective Millennial/next-Gen employees? Do they modify their (web) communication to adapt to Millennials’ career expectations?	(Durocher et al., 2016) [83] (Zhao 2018) [90]
		Is organizational socialization a two-way process with Millennial employees? How do Millennial employees view HRM?
		Do HR managers hold strong generational stereotypes? How do they view Millennials as job applicants? What is the impact of generations on outcomes such as training and promotion decision? What are the mediators (e.g., entitlement, perceptions related to physical capabilities)?	(Perry et al., 2016) [86]
		What is known about Millennials so far, will that hold for the next generation (Gen Z) of potential employees?	(McGinnis Johnson and Ng 2016) [117]
		Do work expectations/preferences/values/skills/abilities change with time and/or country and/or context and/or diverse samples (e.g., industry or student) for Millennials?	(Kuron et al., 2015 [21], Kultalahti et al., 2015 [118], O’Connor and Raile 2015 [119], Brink and Costigan 2015 [120], Papavasileiou and Lyons 2015 [92])
4.	Generations: Critical perspectives	Do people who simultaneously identify as members of different generational groups differ psychologically from those who identify with a single group? Do they demonstrate greater tolerance for other generational groups?	(Lyons and Schweitzer 2017) [23]
		What is the relationship between individuals’ characteristics (personality, attitudinal, other psychological variables) and the degree of their identification with a generational identity?
		Is the term “Millennial”, for example, something of a social meme? Is the awareness, acceptance, and commonality of understanding of generational labels shifting as this social phenomenon continues to gain traction?
		Does social constructionist perspective and lifespan theory provide more complete explanations for age-related change and differences than generational theory?	Rauvola et al., (2019) [24], Rudolf et al., (2018, 2021) [26,27]
		Will measuring the hypothetical historical, cultural or social impact on the individual increase the understanding of generational transmission of variables of interest (e.g., attitudes, values, personality, etc.) as well as increase prediction?	Campbell et al., (2017) [101]
		Will grouping individuals into smaller birth related “microgenerations,” such as 5-year birth cohorts or single-year cohorts lead to gaining some precision over the broad construct of generations?
		With more complex data sets, (e.g., sets that included different ages for each cohort), will other methods such as item response theory (IRT) and growth curve analysis be used to partially tease apart cohort/generation, time period, and birth cohort?
		How and when generational identities are formed, when dis-identification occurs, the effects of generation identification and the strength of identification, and why (or why not) and how individuals enact and cope with generational stereotypes?
		Will accounting for gender, entry into an organization and organizational structural and cultural aspects give situational cues as to how generational identity is primed?	Urik (2017); Van Rossem (2019) [121]
		What is the consciousness, content, and consequences of age meta-stereotypes?
		Do more inductive and flexible approaches to generational research allow the perspective to be retained in research?	(Parry and Urwin 2021) [94]

presents a synthesis of research questions in the four current research fronts identified earlier.

In millennials and ethics, further development of this research front calls on identifying a complete description of millennials’ ethical profile and whether there are contextual similarities/differences in ethics within millennials.

In millennials and organizational behaviour, future research calls for further exploration of the antecedents of workplace behaviour for samples of millennial employees.

In millennials: HR perspective, it will be beneficial to further explore millennials’ attraction to organizations, career expectations, organizational socialization, training and promotion decisions. Moreover, it will be worthwhile to further explore cross-cultural and longitudinal changes in work expectations/preferences/values/skills/abilities for millennials.

In Generations: Critical perspectives, critics have called for the exploration of more complete explanations of the concept of generations by exploring the concept through the social constructionist perspective, lifespan theory and/or more flexible and inductive approaches. They have further called for methodological advancements such as item response theory, growth curve analysis, or hierarchical age–period–cohort models.

5. Discussion

Our article contributes to the understanding of literature on millennials at work by reviewing the literature produced over the past 20 years. This growing body of literature (see Figure 2) is of increasing importance now that the millennial generation has become a substantial and integral part of the workforce and its management.

We utilized bibliometric methods of citation, co-citation and bibliographic coupling analysis, as well as content analysis to answer three research questions. For RQ1 we identified the most important articles, authors, journals, institutions and countries in terms of the number of publications and citations (see Table 1, Table 2, Table 3 and Table 4). Table 1 and Table 2 provide detailed references that the academic community can utilize to study millennials at work. The articles by Twenge, Campbell, Hoffman and Lance [52] and Smola and Sutton [13] are the two most influential articles in terms of TGC/t (see Table 1). The article with the highest LCSe is a millennial-centred article exploring intragenerational differences (see Stream 5) by Ng, Schweitzer and Lyons [54] (Table 2). This further indicates that millennials (and other generations) may be conceptualized as fuzzy social constructs [26,97,101] with individuals differing more from each other within a certain age bracket than across age brackets.

Figure 2 shows several peaks in P_MAW, TLC and TGC that we think might be because of the special issues published by the Journal of Managerial Psychology (JMP) (‘Generational differences at work’, 2008), the Journal of Business and Psychology (JBP) (‘Millennials and the World of Work’, 2010) and the Journal of Social Psychology (JSP) (‘Millennials in the Workplace’, 2019). In addition, Table 3 shows that, interestingly, no journal apart from JMP and JBP seems to be dominating research on millennials at work and it is surprising to see little research published in top-tiered journals such as, for example, the Journal of Management (JOM) (P_MAW = 1). Even more surprising, another top-tiered journal, the Journal of Organizational Behavior (JOB), has published very little research on millennials at work, though the seminal article by Smola and Sutton [13] was published in JOB. Figure 3 confirms our observation. This information may be useful for journal editors who want to encourage research on the millennial generation. The findings related to influential institutions and countries reveal that most of the research on millennials at work has originated from the U.S., which is well ahead of other countries. (A detailed table of influential institutions ranked by P_MAW and citation metrics is available upon request.) This is understandable because the concept of millennials/Generation Y has originated from the West. Researchers from other countries may find this information useful and may be motivated to study the young generations within their cultural context. For RQ2 and RQ3(a), using co-citation and bibliographic coupling, we identified six distinct but interrelated research streams (the historic core of research) and four research fronts (current research) (see Figure 4 and Figure 5).

Lastly, from the review and analysis of the literature, we derived a profile of millennials and future research questions (RQ3(b), Table 5 and Table 6), which may shape the development of generational research. In particular, we believe that the questions put forth in the Generations: Critical perspectives front may be the most important ones to consider by future researchers because criticism of the concept of generations seems to have been reaching a fever pitch lately—so much so that there have even been calls for abandoning generational research completely [24,25,26,27,28], though newer ways have been suggested to approach the concept of generations [94,121]. In the following sub-sections, we expand our interpretations from the answers to RQ3(b), to present the implications for HRM practice and research.

5.1. Implications for HRM Practice

The popular presses’ continual portrayal of generational labels has also led the practitioner media to stereotype individuals within a category by assuming that all generational members possess the same traits, behaviours, and values [22]. For example, Deloitte in their 2020 survey inform employers that environmental stewardship influences loyalty among millennial employees [122]. However, an influential strand of academic research (Research front 4: Generations: Critical perspectives) argues there is no real basis in academic theory or evidence for distinct generational categories such as millennials [94]. However, the pursuit of the mainstream, social and practitioner media seems to outweigh the evidence presented in academic research and employees are still commonly segmented into generational categories such as millennials, presenting the risk that HRM practices become biased by stereotypes. Nonetheless, HRM must seek to derive value from generational research which can help inform strategies for inclusion by providing a better understanding of the dimension of differences that drives diversity. A more flexible and inductive approach, as suggested by Parry and Urwin [94], may be the way to go for HR professionals—an approach that need not associate specific characteristics to particular age groups, but which considers how any changes identified in generational categories can be accommodated to promote inclusion within organizations. As such, even among millennial workers, a one-size-fits-all approach to HR policies and programs may be inappropriate [92]. Because there is very little research evidence to support the idea that a global millennial generation exists, multinational organizations may be advised to view their young workers as a heterogeneous group rather than as stereotypical ‘millennials’. Further, other demographic differences among millennials need to be identified. For example, HR managers seeking to attract millennial employees should be aware that female millennials may be more ethical than males [22]. Further, organizations that have employed millennials at the start of their careers, may legitimately ask now whether these later-career millennials have grown up and settled down with time. Archival and retrospective data, if available to HRM, may be utilized to draw conclusions about them in the earlier stage of their life, or used to study variations within the millennial group based on the amount of work experience in order to be better informed [21,22].

5.2. Implications for HRM Research

Despite the academic criticism on generational research and labelling or categorization, academic research still seems to be investigating millennials and the upcoming generation, Generation Z, under their respective generational labels. To explain our point, we are informed by the WOS alert that, since our literature search on 30 December 2020, 194 articles on millennials have been published as of 7 July 2022 (Results available upon request.). This may be an indication that research scholarship may not be willing to wholly desert generational research as suggested by some commentators [26,28]. The same commentators, however, also note that generations are ubiquitous due to their popular acceptance, but that alternate explanations need to be explored. Thus, we believe that future research hinges on the exploration of critical perspective and ways forward as suggested by, for example, Parry and Urwin [94]. According to Parry and Urwin [94], focusing on the year of birth and the continued use of generational labels or categories, such as millennials, is problematic because it prevents researchers from understanding the impact of contextual changes on the workforce and from considering meaningful individual differences in employees. They suggest that the longitudinal research on generations should adopt a more inductive and flexible approach that does not have to rely on a strict identification and disentanglement of age, period and cohort effects. Their approach proposes the identification of a dynamic that may be generational in nature but does not accept the presumption that such dynamics present only as categorical changes. Thus, in referring to Parry and Urwin, generational research can be retained in HRM. However, according to their approach and in the call for further research from Lyons and Schweitzer [23] and Weber and Urick [22], HRM researchers may ask and explore the question as to whether the generational label millennial is even valid, and whether all millennials are the same. Thus, investigators may shift away from a sole focus on year of birth and investigate other contextual drivers of the difference in attitudes, such as the role of location, gender and ethnic group. To explore the contextual drivers, robust conceptualizations, such as the notion of social location and construction, generational identities, collective memories and lifespan perspectives [1,26,61], need to be incorporated.

Further, while exploring the ethical profile of millennials [73], millennials at work can, for future research, be linked to UN Sustainable Development Goals (SDGs). For example, future research may explore how millennials at work can contribute to sustainable economic growth through innovative business models, entrepreneurship, and employment opportunities (Goal 8: decent work and economic growth); how they view gender equality in the workplace, drive changes in policies and practices, and what more needs to be done to achieve gender balance (Goal 5: Gender equality); how they are changing consumer behaviour and pushing for more sustainable practices in businesses, such as reducing waste, promoting recycling, and using renewable resources (Goal 12: Responsible consumption and production); how they are addressing climate change through their work, for example, by promoting sustainable energy, reducing carbon emissions, and advocating for climate-friendly policies; and how they view education and contribute to the promotion of access to quality education in their workplaces and communities (Goal 4: Quality education).

Finally, in terms of methodology, prior review studies, both those that have explored generations/generational differences and those that have centred on millennials, were traditional reviews. Though traditional reviews benefit from the authors’ expertise in the field, they are also vulnerable to review authors’ specialization-in-the-field biases [38,39]. While few review studies were meta-analyses, they were narrower in scope. For example, Twenge [30] used four time-lagged studies and Costanza, Badger, Fraser, Severt and Gade [5] examined 20 studies to explore intergenerational differences in work attitudes. Our bibliometric review study comprehensively explores the body of literature on millennials at work over the last 20 years and offers context and placement in the literature for prior studies [38]. To the best of our knowledge, no previous review study has performed a bibliometric analysis of literature on millennials at work. Using bibliometrics, our study, therefore, seeks to provide a quick reference guide for researchers interested in research on millennials at work by identifying the historic core structure of research, the current research fronts and subsequently identifying the key authors, articles, journals, institutions and countries and recommending questions to be considered for future research.

6. Limitations and Conclusions

As is usually the case, our study has some limitations. First, while WOS is a reliable database, key non-WOS (Scopus and Google Scholar) articles were not part of our analysis [123]. While going through our content analysis, we did cite key non-WOS articles where relevant [4], though they were not part of our citations analysis, co-citation mapping or our further analysis. Future research may look to combine articles from all the databases and perform a more detailed analysis for each stream. Second, from a methodological point of view, while we utilized the tried and tested technique of co-citation mapping, researchers working on systematic reviews could gain further understanding of the streams emerging within their literature by utilizing other techniques, such as keyword co-occurrence analysis and latent semantic analysis [124]. Additionally, other metrics such as network centrality could be applied to the co-citation network of articles, authors, journals, institutions and countries to identify influential nodes in the network [38]. Third, a problem with using citation-based metrics in bibliometrics is that we cannot account for the Matthew effect and citation cartels [125]. Future bibliometric reviews may want to test for networking, prestige, and appropriateness effects while controlling for unobserved paper characteristics [126].