Amphetamine is a drug that suppresses appetite. In a study of this effect, a pharmacologist randomly allocated 24 rats to three treatment groups to receive an injection of amphetamine at one of two dosage levels (2.5 mg/kg and 5 mg/kg), or an injection of saline solution. She measured the amount of food consumed by each animal in the 3-hour period following the injection. The results (gm of food consumed per kg body weight) are available in amphetamine. dat. Treatment Consumed
1 0.0 112.6
2 0.0 102.1
3 0.0 90.2
4 0.0 81.5
5 0.0 105.6
6 0.0 93.0
7 0.0 106.6
8 0.0 108.3
9 2.5 73.3
10 2.5 84.8
11 0.0 67.3
12 2.5 129
13 2.5 80.7
14 2.5 90.0
15 2.5 75.5
A) Is there evidence that the amount of food consumed by animals is different among the three groups?
B) Test the claim that food consumption is smaller in the group receiving 5.0 mg/kg amphetamine than the group receiving the saline solution.
C) Sketch a plot of the estimated mean food consumption for each group versus amphetamine dosage levels. Describe in a few words the relationship (if any) you observe in this plot.
D) Use a linear trend contrast to test the null hypothesis of no linear trend in food consumption. Report the test statistic and p-value and a conclusion within the context of the data.