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    Hypothesis Testing & Cohen's d

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    13. To evaluate the effect of a treatment, a sample of n = 9 is obtained from a population with a mean of µ = 40, and the treatment is administered to the individuals in the sample. After treatment, the sample mean is found to be M = 33.

    a. If the sample has a standard deviation of s = 9, are the data sufficient to conclude that the treatment has a significant effect using a two-tailed test with ±= .05?
    b. If the sample standard deviation is s = 15, are the data sufficient to conclude that the treatment has a significant effect using a two-tailed test with ±= .05?
    c. Comparing your answer for parts a and b, how does the variability of the scores in the sample influence the outcome of a hypothesis test?

    14. Many animals, including humans, tend to avoid direct eye contact and even patterns that look like eyes. Some insects, including moths, have evolved eye-spot patterns on their wings to help ward off predators. Scaife (1976) reports a study examining how eye-spot patterns affect the behavior of birds. In the study, the 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 walls. 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 ±= .05.

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

    c. Write a sentence that demonstrates how the outcome of the hypothesis test and the measure of
    effect size would appear in a research report.

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    Solution Summary

    The solution provides step by step method for the calculation of testing of hypothesis and Cohen's d. 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.