# Description of Hypothesis Testing, Cohen's d & Effect size

4. Explain why a t distribution tends 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 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 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 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.

18. Other research examining the effects of preschool childcare has found that children who spent time in day care, especially high quality day care, perform better on math and language tests than children who stay home with their mother. Typical results, for example, show that a sample of n= 25 children who attended day care before starting school had and average score of M= 87 with SS= 1536 on a standardize math test for which the population mean u=81 . Is the sample sufficient to conclude that children with a history of preschool day care are significantly different from the general population? Use a two tailed test with a = .01

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#### Solution Summary

The solution provides a step by step method for the calculation of testing of hypothesis, Cohen's d and effect size. Formula for the calculation and interpretations of the results are also included. An interactive excel sheet is included. The user can edit the inputs and obtain the complete results for a new set of data.