# Hypothesis Testing of Mean & Cohen's d

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The spotlight effect refers to overestimating the extent to which others notice your appearance or behavior, especially when you commit a social faux pas. Effectively, you feel as if you are suddenly standing in a spotlight with everyone looking. In one demonstration of this phenomenon, Gilovich, Medvec, and Savitsky (2000) asked college students to put on a Barry Manilow T-shirt that fellow students had previously judged to be embarrassing. The participants were then led into a room in which other students were already participating in an experiment. After a few minutes, the participant was led back out of the room and was allowed to remove the shirt. Later, each participant was asked to estimate how many people in the room had noticed the shirt. The individuals who were in the room were also asked whether they noticed the shirt. In the study, the participants significantly overestimated the actual number of people who had noticed.

a. In a similar study using a sample of n = 9 participants, the individuals who wore the shirt produced an average estimate of M 6.4 with SS 162. The average number who said they noticed was 3.1. Is the estimate from the participants significantly different from the actual number? Test the null hypothesis that the true mean is 3.1 using a two-tailed test with = .05.

b. Is the estimate from the participants significantly higher than the actual number (3.1)? Use a one-tailed test with = .05.

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 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 Cohens 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 o 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 Cohens 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.

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