SPSS exercise 5.1

For the following analysis we'll be using Fields data Viagra.sav. Viagra is a drug used to treat impotence, and nowadays less a taboo, but there was a time when it had to be tested on the effectiveness. In this dataset you'll find the results of a small experiment (n = 15), in which one group of participants was administered a placebo, one group a small dose of Viagra, and one group a high dose. The dependent variable was libido (you can think of an operationalisation (way of measurement) yourself,as long as it's on an interval or ratio scale).

a. Why is an Analysis of Variance (ANOVA) the best analysis to test if the dose of Viagra (independent variable) has an effect on the libido (dependent variable)? Name at least two reasons.

b. Why can't you use an Independent Samples t-test for this analysis?

c. State the null hypothesis and alternative hypothesis in words.

d. Run the ANOVA and describe the mean and standard deviation for all groups.

e. What is the grand mean (the mean of the dependent variable regardless of the group participants are in)?

f. What can you conclude on the basis of these means?

g. Is this result statistically significant?

h. Do all the groups differ significantly from each other? Run (if you haven't already done so), a post-hoc test with Bonferroni correction to examine this. Which three null hypotheses are tested here? Formulate the hypotheses in words and involve the variables and research units in your formulation!

i. What do you conclude on the basis of the multiple comparisons (= post hoc) test?