Benefits of a megastudy approach

[...]one team of researchers might study how giving membership subsidies increases gym attendance at a private gym in Boston, Massachusetts, whereas another research group might investigate the effect of offering gym-attendance incentives to students visiting a university gym in southern California. Because the circumstances - including the location and participants - of these two studies are not the same, it is impossible to conclude whether the results from these studies diverge because of differences in the populations studied or in the efficacy of the interventions. According to the authors' definitions of a megastudy, large numbers of participants from a common pool were allocated to each of the interventions; the interventions had the same 'treatment' and 'follow-up' periods (the periods when and after the intervention was applied), and a standard set of metrics was used to evaluate the effectiveness of the interventions. [...]megastudies do not overcome the challenge of achieving external validity, in that the findings of one megastudy might not generalize to other scenarios that involve other places and people.