Interpreting differences between studies of children and adults goes beyond pharmacokinetic and pharmacodynamic differences. There are major, but often subtle, differences in diagnosis and assessment of outcomes that need to be understood. This is particularly exemplified in studies of autism spectrum disorders, where study methods appear similar. While the studies by Hollander et al. in both age groups used the Autism Diagnostic Interview–Revised and the Autism Diagnostic Observation Schedule, the former requires a parent interview, which was not available for all adult subjects. Also, some adults historically meet the full criteria but have amelioration of symptoms across time and therefore may not meet the full criteria at the time of the evaluation. Additionally, in these studies, essentially the same outcome measure was used across different ages (the compulsion scale of the Yale-Brown Obsessive Compulsive Scale). This has the advantage of being a clinical interview and not a parent or self-report, though the availability and type of other informants are likely to be different across the age range (i.e., more reliance on patient interview in adults and more reliance on parent interview in children). Another issue that is likely common to both groups is difficulty with recruitment. The small study groups make it difficult to identify subgroups of individuals in such heterogeneous samples. This is further compounded by the differences in age ranges in pediatric versus adult studies. The adult study had an age range of 18–60 years (mean age=34.3 years, SD=14.3), whereas the pediatric fluoxetine study had an age range of 5–17 years (mean age=8.2 years, SD=3.0).