# Hypothesis Testing & Cohen's d

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Last fall, a sample of n = 36 freshmen was selected to participate in a new 4-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 freshmen must take the same English Language Skills course, and the mean score on the final example for the entire freshman class was µ = 74. The students in the new program had 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 = .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 = .05.

Birds were tested in a box with two chambers and were free to move from one chamber to another. In one chamber, two large eye-spots were painted on one wall. The other chamber had plain wall. The researcher recorded the amount of time each bird spent in the plain chamber during a 60-minute session. Suppose the study produced a mean of M = 37 minutes on the plain chamber with SS = 288 for a sample of n = 9 birds. (Note: If the eye spots have no effect, then the birds should spend an average of µ = 30 minutes in each chamber.)

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

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

A researcher would like to examine the effects of humidity on eating behavior. It is known that laboratory rats normally eat on 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 at 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 = .05.

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

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##### Solution Summary

The solution provides 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. Interactive excel sheet is included. The user can edit the inputs and obtain the complete results for a new set of data.

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