Tsetse flies are the vectors of human sleeping sickness and animal trypanosomiasis in Africa. The tsetse fly species Glossina palpalis feeds on the blood of a variety of animals, including humans, and an important question is whether the feeding preferences of individuals can be affected by learning.

To investigate this, Bouyer et al. (2007) provided cohorts of male tsetse flies with a first blood meal of either cows or lizards. After two days, the flies were offered a second blood meal of cows only. The data below measure the proportion of flies in each cohort that took a meal from the cows (the remaining individuals chose not to feed).

a. Display the results of the study in a graph.

b. What assumptions must be met before using ANOVA to test for differences between the two treatment groups in the mean proportion of flies taking the second blood meal from cows? In view of your results in part (a), do you see a problem meeting these assumptions?

c. Consider using a transformation to fix the problems identified in part (b). Given the data, what transformation should be attempted first? Try this transformation on the data. Did it fix the problems?

d. Using the transformed data, test whether the means of the two blood-meal groups are different.

Transcribed Image Text:

Treatment: first blood meal LizardLizard Cow Cow Proportion of flies taking second meal from cow 0.66.0.66, 0.58.0.58, 0.52.0.52, 0.37.0.37, 0.35.0.35, 0.34.0.34, 0.290.29 1.00.1.00, 0.98.0.98, 0.97.0.97, 0.96.0.96, 0.87.0.87, 0.830.83