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# Hypothesis Testing & Cohen's d

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Problem Set 1: Chapter 9, problems 4, 12, 14, 22

4. Explain why t distribution tend to be flatter and more spread out than the normal distribution.

12. Last fall, a sample of n = 36 freshmen was selected to participate in a new 4-hour training program: µ = 74; M = 79.4, s = 18.

a. On the basis of these data, can the college conclude that the students in the new program performed significantly better than the rest of the freshman class? Use a one tailed test with ? = .05

b. Can the college conclude that the students in the new program are significantly different from the rest of the freshman class? Use a two-tailed test with ? = .05

14. In the Preview for this chapter, we discussed a study that examined the effect of eye spot patterns on the behaviour of moth eating birds: µ = 30; M = 37, SS = 288, n = 9.

a. Is this sample sufficient to conclude that the eye-spots have a significant influence on the birds' behaviour? Use a two-tailed test with ? = .05.

b. Compute the estimated Cohen's d to measure the size of the treatment effect.

22. A researcher would like to examine the effects of humidity on eating behaviours. It is known that laboratory rats normally eat an average of µ = 21 grams of food each day. The researcher selects a random sample of n = 16 rats and places them in a controlled atmosphere room in which the relative humidity is maintained to 90%. The daily food consumption scores for the rats are as follows:

14, 18, 21, 15, 18, 18, 21, 18
16, 20, 17, 19, 20, 17, 17, 19

a. Can the researcher conclude that humidity has a significant effect on eating behaviour? Use a two tailed test with a alpha value = .05

b. Compute the estimated d and r2 to measure the size of the treatment effect.