Dermatologists' primary recommendation to prevent skin cancer is minimal exposure to the sun. Yet, models used in product advertisements are typically well tanned. Do such advertisements influence a consumer's attitude toward tanning? University of California and California State University researchers designed an experiment to investigate this phenomenon and published their results in Basic and Applied Social Psychology (May 2010). College student participants were randomly assigned to one of three conditions: (1) view product advertisements featuring models with a tan, (2) view product advertisements featuring models without a tan, or (3) view products advertised with no models (control group). The objective was to determine whether the mean attitude toward tanning differs across the three conditions. A tanning attitude index (measured on a scale of 0 to 5 points) was recorded for each participant. The results are summarized in the accompanying table.

a. Identify the type of experimental design utilized by the researchers.
b. Identify the experimental units, dependent variable, and treatments for the design.
c. Set up the null hypothesis for a test to compare the treatment means.
d. The sample means shown in the table are obviously different. Explain why the researchers should not use these means alone to test the hypothesis, part c.
e. The researchers conducted an ANOVA on the data and reported the following results: F = 3.60, p-value = .03. Carry out the test, part c. Use α = .05 to draw your conclusion.
f. What assumptions are required for the inferences derived from the test to be valid?

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Tanned Models with No Models No Tan Models Sample Size Mean Standard Deviation 56 2.40 .85 56 2.11 .73 56 2.50 .82