This article defines an approximate confidence interval for effect size in correlated (repeated measures) groups designs. The authors found that their method was much more accurate than the interval presented and acknowledged to be approximate by Bird. That is, the coverage probability over all the conditions investigated was very close to the theoretical .95 value. By contrast, Bird’s interval could have coverage probability that was substantially below .95. In addition, the authors’interval was less likely than Bird’s method to present an overly optimistic portrayal of the effect. They also examined the operating characteristics of the Bird interval for effect size in an independent groups design and found that, although it is fairly accurate in its approximation of coverage probability, the accuracy of the approximation does vary with the magnitude of the population effect size.
[1]
M. Browne.
PRECISION OF PREDICTION1, 2
,
1969
.
[2]
L. Hedges.
Distribution Theory for Glass's Estimator of Effect size and Related Estimators
,
1981
.
[3]
Leland Wilkinson,et al.
Statistical Methods in Psychology Journals Guidelines and Explanations
,
2005
.
[4]
G. Cumming,et al.
A Primer on the Understanding, Use, and Calculation of Confidence Intervals that are Based on Central and Noncentral Distributions
,
2001
.
[5]
K. Bird,et al.
Confidence Intervals for Effect Sizes in Analysis of Variance
,
2002
.
[6]
L. Harlow,et al.
What if there were no significance tests
,
1997
.