The pesticide DDT causes tremors and convulsions if it is ingested by humans or other mammals. Researchers seek to understand how the convulsions are caused. In a randomized comparative experiment, 6 white rats poisoned with DDT were compared with a control group of 6 un-poisoned rats. Electrical measurements of nerve activity are the main clue to the nature of DDT poisoning. When a nerve is stimulated, its electrical response shows a sharp spike followed by a much smaller second spike. Researchers found that the second spike is larger in rats fed DDT than in normal rats. This observation helps biologists understand how DDT causes tremors. The researchers measured the amplitude of the second spike as a percentage of the first spike when a nerve in the rat's leg was stimulated.

Poisoned rats 12.207 16.869 25.0505 22.429 8.456 20.589

Unpoisoned rats 11.074 9.686 12.064 9.351 8.182 6.642

Normal probability plots show no evidence of outliers or strong skewness. Both populations are reasonably normal, as far as can be judged from 6 observations. The difference in means is quite large, but in such small samples the sample mean is highly variable. A significance test can help confirm that we are seeing a real effect. Because the researchers did not conjecture in advance that the size of the second spike would increase in rats fed DDT, we test

Ho: u1 = u2

Ha: u1 > u2

Carry out the complete significance test