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# Hypothesis Testing, Cohen's d & Effect size

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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 freshman was selected to participate in a new four hour training program designed to improve study skills. To evaluate the effectiveness of the new program, the sample was compared with the rest of the freshman class. All freshman must take the same English Language skills course, and the mean score of the final exam for the entire freshman class population mean = 74. The students in the new program has a mean score of M = 79.4 with a standard deviation of 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 a alpha value = .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 a alpha value = .05

22. A researcher would like to examine the effects of humidity on eating behaviors. It is known that laboratory rats normally eat an average of population mean = 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 behavior? Use a two tailed test with a alpha value = .05

B. Compute the estimated d and percentage of variance accounted for by the treatment (r squared) to measure the size of the treatment effect.