Description

Homework #4

ANOVA

Open the dataset entitled “Gorilla Data.sav”.  This dataset involves a totally unethical experiment conducted by bored, resentful anthropologists to determine if alcohol consumption increases aggression in gorillas.  In all, 20 Western Gorillas (Gorilla=0) and 20 Eastern Gorillas (Gorilla=1) were involved in this heinous experiment (Total N = 40).  These 40 gorillas were randomly assigned to one of three groups.  The first group of gorillas (Group = 0) received no alcoholic beverages.  The second group of gorillas (Group = 1) drank 1 alcoholic beverage.  The third group of gorillas (Group = 2) drank 2 alcoholic beverages.  Excited to finally have something interesting to observe, the anthropologists measured how many times the gorillas threw their feces at zoo patrons after the alcohol was consumed (n_feces).  Then, unsatisfied by their results, the anthropologists conducted a second experiment using a within-subjects design.  On day one, the researchers measured the number of times each gorilla assaulted a fellow gorilla at three separate time points (morning, noon, night). The next day, the researchers repeated the experiment, but this time the researchers gave the gorillas one alcoholic beverage prior to recording the number of assaults at each of the three time points (morningANDalc, noonANDalc, and nightANDalc).

1)      After some initial hesitation (of course), you agree to analyze the anthropologists’ data.  Their first research question involves whether the number of alcoholic beverages consumed affects the number of times the gorillas threw feces at zoo patrons.  Conduct a Univariate ANOVA from the General Linear Model menu using Group as the IV or Factor, and n_feces as the DV.  Under Options (or “EM Means” in SPSS version 25), get the Estimated Marginal Means for Group.  Request a Tukey test for Group. Then, under Plots, request a plot of Group.  Then, interpret the output.  Describe which analysis you performed and why. Then, interpret the F value for the effect of Group (in APA style and in words), and the results of the Tukey test. Be sure to report group means when interpreting the Tukey test.

2)      The anthropologists were also interested in determining whether the relationship between alcohol consumption and feces throwing differed for Western and Eastern gorillas. In other words, did the effect of alcohol on fece-throwing seem stronger for Western or Eastern gorillas?  Conduct a two-way ANOVA, estimating the main effect of Group, the main effect of Gorilla, and the interaction between Group and Gorilla (Group*Gorilla).  Create profile plots (3 in total) of the effect of Group, the effect of Gorilla, and the interaction between Group and Gorilla.  Report the results in APA style. Include in your write-up your interpretation of each of the three F values. Discuss which Group had the highest mean number of fece-tossing behavior, which type of Gorilla was more inclined to throw around feces, and finally whether the relationship between Group and fece throwing differed by type of Gorilla. 

3)      The next research question posed by the anthropologists was whether the number of times the gorillas assaulted other gorillas changed over the course of the three time points  (morning, noon, and night).  Conduct a Repeated Measures ANOVA to test this hypothesis.  Was there evidence of significant change across the 3 time points? Interpret the F value for the main effect of time. Interpret the Pairwise Comparisons, including means at each time point. What does the plot tell you about the gorillas’ aggressive behavior at different times of day?

4)      Finally, conduct a two-way Repeated Measures ANOVA to determine whether there is a main effect of alcohol, a main effect of time, and/or an interaction between alcohol and time. Make sure you interpret all three F values, and describe what is happening in the plot of the interaction.