I might be reading a bit too deep into this, but the source of data for the study titled it as "Fragile Families" (since renamed to "Future of Families") and it

I might be reading a bit too deep into this, but the source of data for the study titled it as "Fragile Families" (since renamed to "Future of Families") and it really makes it sound to me, as a laymen, that the data is skewed towards families that might not be representative of an average family / we might not be able to take much away from this beyond the groups that were actually studied. This is a study about a relationship between mental development and abuse, and it's done with a data source skewed towards low-income families with unmarried parents in large cities. Are these families more likely to be abusive or have ADHD in the first place? Less likely? There's a relevant joke that the results of most psychology studies should have "for college students" appended to it. I think this study needs a similar caveat appended, "Longitudinal study on the relationship between childhood maltreatment and ADHD in low-income unmarried families in large cities." From https://ffcws.princeton.edu/about https://ffcws.princeton.edu/about The Future of Families and Child Wellbeing Study (FFCWS) is based on a stratified, multistage sample of 4898 children born in large U.S. cities (population over 200,000) between 1998 and 2000, where births to unmarried mothers were oversampled by a ratio of 3 to 1. This sampling strategy resulted in the inclusion of a large number of Black, Hispanic, and low-income families. Mothers were interviewed shortly after birth and fathers were interviewed at the hospital or by phone. Follow-up interviews were conducted when children were approximately ages 1, 3, 5, 9, 15, and 22 (began late 2020). When weighted, the data are representative of births in large US cities. Beginning with the baseline interviews in 1998-2000, the core study was originally designed to primarily address four questions of great interest to researchers and policy makers: (1) What are the conditions and capabilities of unmarried parents, especially fathers?; (2) What is the nature of the relationships between unmarried parents?; (3) How do children born into these families fare?; and (4) How do policies and environmental conditions affect families and children?