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Originally Posted By Good article...

I can't believe with all I've read on the subject that I haven't seen that article before. However, how do you explain the following excerpt from the article I posted above?
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"The most conclusive evidence that genetics can contribute to ADHD, however, comes from studies of twins. Jacquelyn J. Gillis, then at the University of Colorado, and her colleagues reported in 1992 that the ADHD risk of a child whose identical twin has the disorder is between 11 and 18 times greater than that of a nontwin sibling of a child with ADHD; between 55 and 92 percent of the identical twins of children with ADHD eventually develop the condition.

One of the largest twin studies of ADHD was conducted by Helene Gjone and Jon M. Sundet of the University of Oslo with Jim Stevenson of the University of Southampton in England. It involved 526 identical twins, who inherit exactly the same genes, and 389 fraternal twins, who are no more alike genetically than siblings born years apart. The team found that ADHD has a heritability approaching 80 percent, meaning that up to 80 percent of the differences in attention, hyperactivity and impulsivity between people with ADHD and those without the disorder can be explained by genetic factors."
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I can only assume these twins (identical & fraternal) were raised by the same parents. Why is there a significantly higher ratio of identical twins both having AD/HD as compared to fraternal? Seems to me like it'd be a pretty compelling argument for a genetic factor.