Dear Colleagues,

Real world evidence (RWE) means evidence obtained from real world data (RWD), which are observational studies based on real data obtained from daily clinical practice. Specifically, RWD could be defined as studies that collect data relevant to human health that do not come from conventional randomized clinical trials. Randomized controlled clinical trials (RCTs) are the gold standard for determining the efficacy and safety of a therapy. In fact, and as is known, RCTs constitute the research design with greater internal validity. In this sense, they are prospective, have definite results a priori, are characterized by randomization and control of the groups, apply standardized health interventions to the selected patients, blind the entire design to obtain results without risk of bias, etc.. However, they have at least two limitations. They usually limit themselves to evaluating specific interventions one by one. Second, when selecting the patient sample according to strict inclusion and exclusion criteria, they have reduced external validity (or generalization), which limits the transfer of their results. It is these limitations that determine the utility of RWD and RWE. They document the real care that patients receive in the clinic and include a variety of cases (for example, patients suffering from several diseases at once) without limiting strict inclusion and exclusion criteria. They can generate long-term data on the effectiveness and safety of health interventions, in addition to providing useful information for economic health analyses. RWD and RWE provide the external validity that RCTs lack. In fact, the main advantage of RWD and RWE, in addition to a lower cost, larger sample size, and greater representativeness than other research designs, is their high external validity. Although most RWE and RWD studies have focused on the use and potential benefits or risks of a medical product, their potential in other areas and objectives is very broad. Precisely for this reason, in this Special Issue, we intend to expand them, and we hope to have RWE and RWD studies in epidemiology in general, and in particular in environmental and cancer epidemiology, as well as in clinical research, among others.

Dr. Maria A Barceló
Guest Editor

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• real world data
• real world evidence
• environmental epidemiology
• clinical epidemiology