Question

Toxaphene is an insecticide that has been identified as a pollutant in the Great Lakes ecosystem. To investigate the effect of toxaphene exposure on animals, groups of rats were given toxaphene in their diet. A study reports weight gains (in grams) for rats given a low dose (4 ppm) and for control rats whose diet did not include the insecticide. The sample standard deviation for 23 female control rats was 33 g and for 19 female low-dose rats was 56 g. Does this data suggest that there is more variability in low-dose weight gains than in control weight gains? Assuming normality, carry out a test of hypotheses at significance level .05. (Give f to 2 decimal places and the p-value to 3 decimal places.)

f	=
P-value

Answer 1

Let denote the variance for control rats and low dose rats respectively.

The null and alternate hypothesis are:

H0:

Ha:

The test statistic is given by:

Since this is a left-tailed test, so the p-value is given by:

Since p-value is less than 0.05, so we have sufficient evidence to reject the null hypothesis H0.

Thus we can conclude that there is more variability in low-dose weight gains than in control weight gains.