Our bodies have a natural electrical field that is known to help wounds heal. Does changing the field strength slow healing? A series of experiments with newts investigated this question. In one experiment, the two hind limbs of 12 newts were assigned at random to either experimental or control groups. This is a matched pairs design.
The electrical field in the control limbs was reduced to zero by applying a voltage. The "experimental" limbs were left alone, so that they still had the natural electric field.
If it is true that the electric field helps healing, than the healing times for the control group should be bigger than the healing times for the experimental group. Here are the rates at which new cells closed a razor cut in each limb, in micrometers per hour:
Carry out a t-test to see if the mean healing rate is significantly lower in the experimental limbs, including all 12 newts. What are the test statistics and their P-values?