In the problems at the end of Chapter 8, we presented a study indicating that people with visible tattoos are viewed more negatively than people without visible tattoos (Resenhoeft, Villa, & Wiseman, 2008). Suppose that a researcher intends to examine this phenomenon by asking participants to rate the attractiveness of women in a series of ten photographs. For one group of participants, none of the women has any visible tattoos. For a second group, however, the researcher modified one of the photographs by adding a tattoo of a butterfly on the woman's left arm. Using a 7-point rating scale, the n = 15 participants who viewed the photograph with no tattoo gave the woman an average rating of M = 4.9 with SS = 15.0. The n = 15 participants who saw the photograph with a tattoo gave the same woman an average rating of M = 4.2 with SS = 18.6.
a. Does the existence of a tattoo have a significant effect on the attractiveness rating of the woman in the photograph? Use a two-tailed test with α =.05.
b. Compute r2, the percentage of variance accounted for by the treatment, to measure the effect size.
c. Write a sentence describing the outcome of the hypothesis test and the measure of effect size as it would appear in a research report.