Conditioning on "study" is essential for valid inference when combining individual data from multiple randomized controlled trials: a comment on Reesor et al's School-based weight management program curbs summer weight gain among low-income Hispanic middle school students

Abstract

Considering the need for examining summertime versus school year weight gain among children, we read with interest the paper, “School-based weight management program curbs summer weight gain among low-income Hispanic middle school students.” We were intrigued by the conclusion that “a school-based weight management program protected overweight/obese students against potentially greater summer weight gain.” We commend the authors for recognizing the importance of aggregating individual participant data (IPD) from several randomized controlled trials (RCTs) to allow for stronger causal inferences and obtain an adequate sample size. We note, however, 2 critical concerns that raise doubts about the veracity of the results: the authors appear to have ignored “study” as a factor in their analysis, and the sample sizes do not appear to match those in the original studies.