Debating ADHD's causes
THE BARKLEY/MOFFITT ADHD debate presented in the July/August Monitor "Letters" section demonstrates why the debate about parent versus child effects for ADHD will go on without end, at least until the full range of data are considered. In short, they are both right (correlation by itself does not demonstrate cause) and they are both wrong (child genes cause ADHD symptoms).
Many studies now demonstrate that reporter biases strongly affect the interpretation of correlational findings, including those of twin studies. Various models can be constructed to deal with this, but they do not agree. The only solution is to use measurement techniques that are free of reporter bias. However, I know of only three twin studies for ADHD that use blind, well-trained observers. More are needed.
Second, cause is only adequately demonstrated in manipulation experiments. Presently, I am aware of five or six that specifically target parental behavior in a risk population before the appearance of diagnosable ADHD. All have been successful in stopping the acquisition of ADHD behavior over a period of at least a year and in some cases much longer. More of these are also needed.
Perhaps both child (genes) and parent effects (maybe also genes) cause ADHD. When a full range of data are available, the debate will move forward.
STEVEN A. McFADYEN-KETCHUM, PHD Vanderbilt University