Research conducted by: Pearson et al. (2003, see reference below)

Case study prepared by: David Lane and Emily Zitek

Overview

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 testing.

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).

D0 D15 D30 D60

57 48 64 62

27 42 48 49

32 39 34 30

31 23 25 34

34 36 42 38

38 34 40 36

71 61 59 77

33 36 42 51

34 41 36 45

53 57 67 42

36 32 29 43

42 48 50 57

26 48 44 36

52 39 57 58

36 36 36 35

55 48 57 60

36 35 30 33

42 39 36 49

36 32 41 33

54 48 65 59

34 35 35 35

29 28 40 37

33 27 43 45

33 40 44 29

Design Issues
This is a repeated-measures design because each participant performed the task after each dosage.

Descriptions of Variables

The link to the ADHD case study http://onlinestatbook.com/2/case_studies/adhd.html

69.       A researcher wants to know if the mean times (in minutes) that people watch their favorite news station are the same.  Suppose that Table 13.24 shows the results of a study.

Assume that all distributions are normal, the four population standard deviations are approximately the same, and the data were collected independently and randomly.  Use a level of significance of 0.05.