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A Note on Interpretation of the Paired-Samples t Test
Donald W. Zimmerman
Journal of Educational and Behavioral Statistics
Vol. 22, No. 3 (Autumn, 1997), pp. 349-360
Stable URL: http://www.jstor.org/stable/1165289
Page Count: 12
You can always find the topics here!Topics: T tests, Correlations, Degrees of freedom, Significance level, False positive errors, Experiment design, Simulations, Observational research, Population mean, False negative errors
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Explanations of advantages and disadvantages of paired-samples experimental designs in textbooks in education and psychology frequently overlook the change in the Type I error probability which occurs when an independent-samples t test is performed on correlated observations. This alteration of the significance level can be extreme even if the correlation is small. By comparison, the loss of power of the paired-samples t test on difference scores due to reduction of degrees of freedom, which typically is emphasized, is relatively slight. Although paired-samples designs are appropriate and widely used when there is a natural correspondence or pairing of scores, researchers have not often considered the implications of undetected correlation between supposedly independent samples in the absence of explicit pairing.
Journal of Educational and Behavioral Statistics © 1997 American Educational Research Association