depressedr 2. Sigall and Ostrove (1975) did an experiment to assess whether the

Question

depressedr 2. Sigall and Ostrove (1975) did an experiment to assess whether the physical attractiveness of a defendant on trial for a crime had an effect on the severity of the sentence given in mock jury trials. Each of the participants in this study was randomly assigned to one of the following three treatment groups; every participant received a packet that described a burglary and gave background information about the accused person. The three treatment groups differed in the type of information they were given about the accused person's appear- ance. Members of Group 1 were shown a photograph of an attractive person; members of Group 2 were shown a photograph of an unattractive person; members of Group 3 saw no photograph. Some of their results are described here. Each participant was asked to assign a sentence (in years) to the accused person; the researchers predicted that more attractive persons would receive shorter sentences a. Prior to assessment of the outcome, the researchers did a manipulation 4 check. Members of Groups 1 and 2 rated the attractiveness (on a 1 to 9 scale, with 9 being the most attractive) of the person in the photo. They reported that for the attractive photo, M = 7.53; for the unattractive photo, M = 3.20, F( 1,108) = 184.29. Was this difference statistically significant (using = .05)? b. What was the effect size for the difference in (2a)? c. Was their attempt to manipulate perceived attractiveness successful? d, why does the F ratio in (2a) have just df=l in the numerator? e. The mean length of sentence given in the three groups was as follows: 5 Group 1: Attractive photo, M = 2.80 Group 2: Unattractive photo, M = 5.20 Group 3: No photo, M = 5-10

Explanation / Answer

a) The p value for F( 1,108) = 184.29 is less than 0.0001

The difference is considered extremely significant (as p value is much less than 0.5)

b) effect size = 7.53-3.20= 4.33

c) yes, as the difference is significant, there is enough evidence to conclude that to manipulate perceived attractiveness is successful

d) F is the ratio between mean square error between groups and within groups, since the test is between two groups, the numerator degrees of freedom ( df) is 2-1= 1

e) difference is significant as p value is less than 0.025 which is much less than 0.05

Yes overall F would also have been significant ( as F for group 1 and 2 is significant, then if it is not significant for group 2 and 3 also , the overall will be significant, we can clearly see that it would also be significant among group 1 and 3)

f) yes ,as the difference is significant, attractiveness have an effect on length of sentence

g) effect size = 5.20-2.80 = 2.4

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