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The Pediatric Forum
November 2002

Overstating the Behavioral Effects of the Seattle Social Development Project

Arch Pediatr Adolesc Med. 2002;156(11):1155. doi:

I would like to raise 2 issues regarding a recent report of the effects of the Seattle Social Development Project (SSDP) on sexual behavior and an accompanying editorial in the ARCHIVES.1,2

First, the article reports data from 144 subjects (the "full-intervention" group) who participated in the SSDP program in grades 1 through 4 as part of a randomized experiment and continued in the intervention condition in fifth grade when the study changed to a quasi experiment. The article states that the SSDP has exhibited "consistently high sample retention rates," with 93% of subjects followed up at age 21 years. For the full-intervention group, the follow-up rate was calculated using the 156 fifth-graders who had parental consent to participate in the quasi experiment as a "baseline." However, involvement of these subjects in the study commenced 4 years earlier. Previous reports from the SSDP do not give the sample size of the full-intervention group at the first-grade baseline, but show that at the second grade follow-up, it comprised 285 subjects.3 Thus, the correct follow-up rate for the full-intervention group at age 21 years was no more than 50%. This low retention rate seriously undermines the methodological integrity of the evaluation.