Effects of a Drug on Cognitive Functioning in Children with Mental
Retardation and ADHD
Research conducted by: Pearson
et al. (2003, see reference below)
Case study prepared by: David
Lane and Emily Zitek
This study investigated the cognitive effects of stimulant medication
in children with mental retardation and Attention-Deficit/Hyperactivity
Disorder. This case study shows the data for the Delay of Gratification
(DOG) task. Children were given various dosages of a drug, methylphenidate
(MPH) and then completed this task as part of a larger battery
of tests. The order of doses was counterbalanced so
that each dose appeared equally often in each position. For
example, six children received the lowest dose first, six received
it second, etc. The children were on each dose one week before
This task, adapted from the preschool delay task of the Gordon
Diagnostic System (Gordon, 1983), measures the ability to suppress
or delay impulsive behavioral responses. Children were told that
a star would appear on the computer screen if they waited “long
enough” to press a response key. If a child responded sooner
in less than four seconds after their previous response, they
did not earn a star, and the 4-second counter restarted. The DOG
differentiates children with and without ADHD of normal intelligence
(e.g., Mayes et al., 2001), and is sensitive to MPH treatment
in these children (Hall & Kataria, 1992).
Questions to Answer
dosage lead to higher cognitive performance (measured by the number
of correct responses to the DOG task)?
This is a repeated-measures
design because each participant performed the task after each
Descriptions of Variables
||Number of correct responses after taking a placebo
||Number of correct responses after taking .15 mg/kg of the
||Number of correct responses after taking .30 mg/kg of the
||Number of correct responses after taking .60 mg/kg of the
Gordon M (1983), The Gordon Diagnostic
System. DeWitt, NY: Gordon Systems
Hall CW, Kataria S (1992), Effects of
two treatment techniques on delay and vigilance tasks with
attention deficit hyperactive disorder (ADHD) children.
J Psychol 126:17-25
Mayes SD, Calhoun SL, Crowell, EW (2002),
The Gordon Diagnostic System and WISC-III Freedom from
Distractibility index: Validity in identifying clinic-referred
children with and without ADHD. Psychol Rep ,91,
Pearson DA, Santos CW, Roache JD, Casat
CD, Loveland KA, Lachar D, Lane DM, Faria, LF, Cleveland
LA (2003), Treatment effects of methylphenidate on behavioral
adjustment in children with mental retardation and ADHD. J
Am Acad Child Adolesc Psychiatry, 42, 209-216.
Pearson, D.A., Santos,
C.W., Jerger, S.W., Casat, C.D., Roache, J., Loveland,
K.A., Lane, D.M., Lachar, D., Faria, L.P., & Getchell,
C. (2003) Treatment effects of methylphenidate on cognitive
functioning in children with mental retardation and ADHD.
Journal of the American Academy of Child and Adolescent
- What is the independent variable of this experiment?
How many levels does it have?
- What is the dependent variable? On what scale (nominal,
ordinal, interval, ratio) was it measured?
- Create a line graph of the data. Do certain dosages
appear to be more effective than others?
- What is the mean number of correct responses of the
participants after taking the placebo (0 mg/kg)?
- Create a stem and leaf plot of the number of correct
responses of the participants after taking the placebo
(d0 variable). What can you say about the shape of the
- Create a normal quantile plot of d0. What does it tell
you and what aspect of the plot reveals this information?
- What are the standard deviation and the interquartile
range of the d0 condition?
- What is the correlation between the participants' correct
number of responses after taking the placebo and their
correct number of responses after taking 0.60 mg/kg of
- Perform a repeated measures ANOVA.
- How many degrees of freedom does the independent variable
- What are the F and p values?
- Does the performance of the children on the DOG task
differ depending on the dose?
- Test the difference between the d0 and d60 conditions
using a sign test.