In a study of the effect of amphetamine on water consumption, a pharmacologist injected four rats with amphetamine and four with saline as controls. She measured the amount of water each rat consumed in 24 hours. The following are the results, expressed as ml water per kg body weight:

(a) Use a t test to compare the treatments at α = 0.10. Let the alternative hypothesis be that amphetamine tends to suppress water consumption.
(b) Use a Wilcoxon-Mann-Whitney test to compare the treatments at α = 0.10, with the directional alternative that amphetamine tends to suppress water consumption.
(c) Why is it important that some of the rats received saline injections as a control? That is, why didn't the researchers simply compare rats receiving amphetamine injections to rats receiving no injection?

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Amphetamine Control 118.4 124.4 169.4 105.3 122.9 162.1 184.1 154.9