# solution

Eyewitnesses and mugshots. Refer to the Applied Psychology in Criminal Justice (April 2010) study of mugshot choices by eyewitnesses to a crime, Exercise 9.78 (p. 583). Recall that a sample of 96 college students was shown a video of a simulated theft, then asked to select a mugshot that most closely resembled the thief. The students were randomly assigned to view either 3, 6, or 12 mugshots at a time, with 32 students in each group. The number of students in the 3-, 6-, and 12-photos-per-page groups who selected the target mugshot were 19, 19, and 15, respectively.

a. For each photo group, compute the proportion of students who selected the target mugshot. Which group yielded the lowest proportion?

b. Create a contingency table for these data, with photo group in the rows and whether or not the target mugshot was selected in the columns.

c. Analyze the contingency table, part b. Are there differences in the proportions who selected the target mugshot among the three photo groups? Test using Â = .10.

Exercise 9.78

Eyewitnesses and mugshots. Criminologists investigated whether mugshot group size (the number of mugshots shown at one time) has an effect on selections made by an eyewitness to a crime (Applied Psychology in Criminal Justice, April 2010). A sample of 90 college students was shown a video of a simulated theft. Shortly thereafter, each student was shown 180 mugshots and asked to select a photo that most closely resembled the thief. (Multiple photos could be selected.) The students were randomly assigned to view either 3, 6, or 12 mugshots at a time. Within each mugshot group size, the students were further randomly divided into three sets. In the first set, the researchers focused on the selections made in the first 60 photos shown; in the second set, the focus was on selections made in the middle 60 photos shown; and in the third set, selections made in the last 60 photos were recorded. The dependent variable of interest was the number of mugshot selections. Simulated data for this 3 Â 3 factorial ANOVA, with mugshot group size at three levels (3, 6, or 12 photos) and photo set at three levels (first 60, middle 60, and last 60) are saved in the accompanying file. Fully analyze the data for the researchers. In particular, the researchers want to know if mugshot group size has an effect on the mean number of selections, and, if so, which group size leads to the most selections. Also, are there a higher number of selections made in the first 60, middle 60, or last 60 photos viewed?

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