Rather it requires the willingness to consider the data from a common sense perspective. The most ecologically valid means of understanding a child is to live with him. As clinicians and educators, we rarely, if ever, have that luxury, except with our children. The second most valid way is to obtain a thorough history from parents or caregivers. Although these individuals may not possess our diagnostic or clinical framework for data analysis, history is our best ally for initial case formulation and the generation of diagnostic hypotheses.
Life is complicated.
I would like to add, however, that it does affect probability. Thus, although biology may set and define the boundaries of each individual's playing field of life, experience and the unique ways each of us thinks are a powerful phenomenon in affecting life outcome. The work of Emmy Werner and others has very powerfully demonstrated this fact. ADHD may predispose individuals to behave in certain ways, however, it does not guarantee that they will or will not turn out in certain ways as adults. Although we learn much as scientists by comparing different groups of children, as the applied behavioral analysts remind us, each individual is unique and each individual must comprise their own experiment.