Psychologists often rely on grouping participants together based on shared characteristics (e.g., are girls better than boy in reading ability). The goal is to broadly understand the relationships between potential causes and effects, and, ideally learn from them. In the first example above, perhaps reading interventions targeting boys may be an effect if the study documents a gender difference in that direction. The problem is that some people may mistake such findings to indicate that ALL girls are better at reading than ALL boys. What is happening statistically is that the researchers are comparing the groups overall, and examining whether the average of a group is different from the group taking into account the dispersion of scores.
These situations get especially touchy when people talk about sensitive topics. One infamous example was the controversy stirred by a 1998 article in Psychological Bulletin, a top research journal in the field. This paper by Rind, Bauserman, and Tromovitch used a technique called meta-analysis, in which multiple individual research studies were combined, to examine the long-term impact of childhood sexual abuse (CSA). The authors concluded that: “Self-reported reactions to and effects from CSA indicated that negative effects were neither pervasive nor typically intense, and that men reacted much less negatively than women. The college data were completely consistent with data from national samples. Basic beliefs about CSA in the general population were not supported.”

Reactions to this paper were intense, however, leading to Congress condemning the study and passing a resolution that unanimously declared sexual relations between children and adults are abusive and harmful. Although the authors were careful to say that simply because CSA may not be particularly harmful to some individuals, the acts are immoral. The debate on this study is quite lengthy, and I recommend further reading. While most subsequent literature supports the general notion that experiencing CSA is bad for one’s physical and emotional health, the use of grouping individual perspectives in trying to find one true answer may not always be the best method, given the diversity of reactions to events.