# Empirical Direction in Design and Analysis

By Norman H. Anderson | Go to book overview

EXERCISES FOR CHAPTER 12

a. Trimming
a1. Consider the numerical example of trimming in Table 12.1.
 1 By visual inspection, show that A1 and A2 have equal trimmed variance. 2 By visual inspection, how will the trimmed mean for A2 change if the 24 is changed to 24,000,000? 3 By visual inspection, how will the width of the confidence interval for the trimmed mean for A2 change if the 24 is changed to 24,000,000? 4 Use the calculations given in the table to show that the standard deviation of a trimmed mean is 1.14.
a2. In Table 12.1, suppose three scores were trimmed in each tail.
 1 In the trimmed Anova, which calculations would remain the same? Does this hold in general, or is it peculiar to these samples? 2 What calculations would change?
a3. The following scores represent number of successful responses in 30 trials on verbal concepts by two groups of 7 dyslexic children, obtained by Q in her thesis research.
 1 Get F for the untrimmed data. 2 Trim two scores in each tail and show that F = 10.71. 3 Get the 95% confidence interval for the mean trimmed difference. 4 What major empirical questions are raised by the two scores of 0?
a4. Q was uncertain about what trimming proportion to use. So she tried all three of.10,.20, and.30. All three yielded a barely statsig F.
 1 What should Q do? 2 What should be Q's main concern in planning any replication?

a5. Draw a graph of a two-humped symmetrical distribution to show why the trimmed and untrimmed means have equal expected value.

b. Rank Tests.

b1. Two teaching techniques for parents of autistic children are compared in the graph of Exercise 3 of Chapter 3. Get ranks for the two groups from this graph and do rank Anova.

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