shows the results of David's functional analysis with and without MPH. During the initial MPH phase, David displayed a low rate of disruptive behavior in all conditions (M
0.13 responses per minute). When David did not receive MPH, high rates of disruptive behavior occurred exclusively in the attention condition (M
2.73). During the reversal to the MPH phase, David again exhibited low rates of disruptive behavior in all conditions (M
0.40), with all disruptive behavior occurring in the first session of the attention condition. Finally, when the no-MPH phase was replicated, David again displayed a high rate of disruptive behavior only in the attention condition (M
Responses per minute of disruptive behavior with and without MPH during the functional analysis.
These results replicated those of Northup, Jones, et al. (1997)
by demonstrating that MPH decreases the relative reinforcing effectiveness of attention. In addition, these results also extend the published literature by extending Northup, Jones, et al.'s findings to persons with both moderate mental retardation and ADHD. This result is significant because, to date, no replications or extensions of Northup et al.'s research on the potential for interaction between MPH and specific environmental variables have been published.
The results of our study should be interpreted with caution for several reasons. First, the results are from a single subject. Second, the current study does not meet all the contemporary research criteria for examining drug—behavior interactions in persons with developmental disabilities (see Napolitano et al., 1999
, for a description of suggested criteria). For example, a double-blind control procedure was not used. That is, the experimenters were aware when the participant had taken his MPH. However, the people who served as reliability observers were blind to the conditions, and the high interobserver agreement suggests that experimenter bias was not an extraneous variable that affected the results.
In conclusion, the results of this study extend the literature on drug treatments for ADHD by showing that functional analyses can generate information on potentially clinically significant interactions between medication and specific environmental variables.