In a study of DDT poisoning, researchers fed several rats a measured amount of DDT. They then made measurements on the rats' nervous systems that might explain how DDT poisoning causes tremors. One important variable was the "absolutely refractory period," the time required for a nerve to recover after a stimulus. This response varies normally. Measurements on four rats gave the following data in milliseconds:
1.3, 1.4, 1.5, 1.6
Suppose that the mean "absolutely refractory period" for unpoisoned rats is known to be 1.3 milliseconds. DDT poisoning should slow nerve recovery and so increase this period.
Do the data give good evidence for this supposition?
Carry out the appropriate test. Giving the P-value, and then interpret the result in the plain language of the context.