Next Article in Journal
The Effect of PM2.5 from Household Combustion on Life Expectancy in Sub-Saharan Africa
Previous Article in Journal
Taking a Gamble for High Rewards? Management Perspectives on the Value of Mental Health Peer Workers
Article Menu
Issue 4 (April) cover image

Export Article

Open AccessArticle
Int. J. Environ. Res. Public Health 2018, 15(4), 747; https://doi.org/10.3390/ijerph15040747

Active (Opt-In) Consent Underestimates Mean BMI-z and the Prevalence of Overweight and Obesity Compared to Passive (Opt-Out) Consent. Evidence from the Healthy Together Victoria and Childhood Obesity Study

1
Global Obesity Centre, Centre for Population Health Research, Deakin University, 1 Gheringhap Street, Geelong, VIC 3220, Australia
2
Biostatistics Unit, Deakin University, Geelong, VIC 3220, Australia
3
Australian Health Policy Collaboration, Victoria University, Melbourne, VIC 8001, Australia
4
Australian Institute of Musculoskeletal Science, The University of Melbourne and Western Health, St Albans, VIC 3021, Australia
5
School of Population Health, University of Auckland, Auckland 1142, New Zealand
*
Author to whom correspondence should be addressed.
Received: 7 February 2018 / Revised: 4 April 2018 / Accepted: 4 April 2018 / Published: 13 April 2018
(This article belongs to the Section Health Behavior, Chronic Disease and Health Promotion)
View Full-Text   |   Download PDF [2532 KB, uploaded 3 May 2018]   |  

Abstract

Background: Tracking population trends in childhood obesity and identifying target areas for prevention requires accurate prevalence data. This study quantified the magnitude of non-participation bias for mean Body Mass Index-z scores and overweight/obesity prevalence associated with low (opt-in) compared to high (opt-out) participation consent methodologies. Methods: Data arose from all Local Government Areas (LGAs) participating in the Healthy Together Victoria Childhood Obesity Study, Australia. Primary schools were randomly selected in 2013 and 2014 and all Grades 4 and 6 students (aged approx. 9–12 years) were invited to participate via opt-in consent (2013) and opt-out consent (2014). For the opt-in wave N = 38 schools (recruitment rate (RR) 24.3%) and N = 856 students participated (RR 36.3%). For the opt-out wave N = 47 schools (RR 32%) and N = 2557 students participated (RR 86.4%). Outcomes: differences between opt-in and opt-out sample estimates (bias) for mean BMI-z, prevalence of overweight/obesity and obesity (alone). Standardized bias (Std bias) estimates defined as bias/standard error are reported for BMI-z. Results: The results demonstrate strong evidence of non-participation bias for mean BMI-z overall (Std bias = −4.5, p < 0.0001) and for girls (Std bias = −5.4, p < 0.0001), but not for boys (Std bias = −1.1, p = 0.15). The opt-in strategy underestimated the overall population prevalence of overweight/obesity and obesity by −5.4 and −4.5 percentage points respectively (p < 0.001 for both). Significant underestimation was seen in girls, but not for boys. Conclusions: Opt-in consent underestimated prevalence of childhood obesity, particularly in girls. Prevalence, monitoring and community intervention studies on childhood obesity should move to opt-out consent processes for better scientific outcomes. View Full-Text
Keywords: obesity prevalence; BMI; active consent; passive consent; non-participation bias; childhood; school obesity prevalence; BMI; active consent; passive consent; non-participation bias; childhood; school
Figures

Figure 1

This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
SciFeed

Share & Cite This Article

MDPI and ACS Style

Strugnell, C.; Orellana, L.; Hayward, J.; Millar, L.; Swinburn, B.; Allender, S. Active (Opt-In) Consent Underestimates Mean BMI-z and the Prevalence of Overweight and Obesity Compared to Passive (Opt-Out) Consent. Evidence from the Healthy Together Victoria and Childhood Obesity Study. Int. J. Environ. Res. Public Health 2018, 15, 747.

Show more citation formats Show less citations formats

Note that from the first issue of 2016, MDPI journals use article numbers instead of page numbers. See further details here.

Related Articles

Article Metrics

Article Access Statistics

1

Comments

[Return to top]
Int. J. Environ. Res. Public Health EISSN 1660-4601 Published by MDPI AG, Basel, Switzerland RSS E-Mail Table of Contents Alert
Back to Top