diction improved when comparing the normal group to the general diagnostic group (ADHD and ADD groups combined). In this regard, the accuracy of classification improved to 67 percent. Mulkins also reported that while findings did not allow for any distinguishment between ADD and ADHD conditions, they did suggest that mothers who report several medical conditions and/or several at-risk conditions, smoking and stress, during their pregnancy are more likely to have children that will be diagnosed as either ADHD or ADD.
However, despite certain similarities between the conditions, there are studies showing some relatively strong differences between the two conditions. One difference between the two conditions is that there are indications that ADD and ADHD may both be related to other disorders but that they are related in differential proportions.
With respect to the foregoing, Knell and Comings (1993) explored the relationship between Tourette's syndrome (TS), chronic tics, and ADD/ADHD. Findings indicated that of the relatives with TS, 61% had AD
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