Last weekend I was reading on the topic of widely cited psychologists. Hans Eysenck was near the top of the list and so I read a little bit about him. Among the things I found was this article, which while not exactly complimentary, did talk about the link between cortical under-arousal and ADHD. After some additional research, it seems that at least a many (but not all) instances of ADHD can be explained by a chronic lack of cortical arousal.
That insight triggered something in my memory...a quick google search turned up this rather aggressive post, which coincides with my memory. Essentially...TV watching inhibits brain activity. Overall...that makes for a pretty interesting correlation.
TV watching has gone up as the rate of ADHD has gone up. I would bet someone could get a dissertation out of the correlation (or lack thereof) between TV watching and ADHD. Multi-country studies showing the penetration of TV vs. the incidence of ADHD? Historical data on ADHD vs. TV in the US...in some other countries for which we have the data?
IF the under-arousal theory of ADHD still has adherents
IF the TV implies lower brain arousal hypothesis is still supported
A. The correlation between ADHD and TV should be evident
B. The causation chain would be ... TV watching --> lower cortical arousal --> ADHD.