Question

Poisoning by the pesticide DDT causes tremors and convulsions. In a study of DDT poisoning, researchers fed several rats a measured amount of DDT. They then measured electrical characteristics of the rats' nervous system that might explain how DDT poisoning causes tremors. One important variable was the "absolute refractory period"—the time required for a nerve to recover after a stimulus. This period varies Normally. Measurements of the absolute refractory period, in milliseconds, for four rats were 1.7, 1.8, 1.9, and 2.0.

Part A: Find the mean refractory period x and the standard error of the mean. (2 points)

Part B: Calculate a 90% confidence interval for the mean absolute refractory period for all rats of this strain when subjected to the same treatment. (4 points)

Part C: Suppose the mean absolute refractory period for unpoisoned rats is known to be 1.3 milliseconds. DDT poisoning should slow nerve recovery and thus increase this period. Do the data give good evidence for this supposition? What can you conclude from a hypothesis test? Justify your response with statistical reasoning. (4 points) (10 points)

Answer 1

a)

standard error = sd/sqrt(n)

	1.7
	1.8
	1.9
	2
mean	1.85
sd	0.129099
n	4
standard error	0.06455

b)

df =n-1 = 3

t =t.inv.2t(0.1,3)

	t	2.353363
	lower	1.698091
	upper	2.001909

90% confidence interval

= (1.6891,2.0019)

c)