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Zimmerman, Donald W. – Journal of Educational Measurement, 2009
This study was an investigation of the relation between the reliability of difference scores, considered as a parameter characterizing a population of examinees, and the reliability estimates obtained from random samples from the population. The parameters in familiar equations for the reliability of difference scores were redefined in such a way…
Descriptors: Computer Simulation, Reliability, Population Groups, Scores
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Zimmerman, Donald W. – Journal of Experimental Education, 1992
The power functions of Student t tests performed on initial scores, ordinary ranks, 3 kinds of modular ranks, and dichotomies were investigated for 1 normal and 3 nonnormal distributions using 2 samples of 26 simulated scores each. Advantages of extending the rank transformation concept are discussed. (SLD)
Descriptors: Computer Simulation, Nonparametric Statistics, Power (Statistics), Scores
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Zimmerman, Donald W. – Journal of Experimental Education, 1995
It is argued that outlier-prone distributions reduce the power of nonparametric tests, but power can be restored through procedures usually associated with parametric tests. Computer simulation is used to show how an outlier detection and downweighting procedure augments the power of the t-test and the Wilcoxon-Mann-Whitney test. (SLD)
Descriptors: Computer Simulation, Identification, Nonparametric Statistics, Power (Statistics)
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Zimmerman, Donald W.; And Others – Journal of Experimental Education, 1992
D. W. Zimmerman argues that the interpretation by J. D. Gibbons and S. Chakraborti of recent simulation results and their recommendations are misleading and suggests use of an alternate test when homogeneity of variance and normality are violated. Gibbons and Chakraborti review their differences with Zimmerman's position. (SLD)
Descriptors: Computer Simulation, Research Methodology, Research Reports, Sample Size