A disadvantage of the experimental design in Example 8 on weight change in anorexic girls is that girls could change weight merely from participating in a study. In fact, girls were randomly assigned to receive a therapy or to serve in a control group, so it was possible to compare weight change for the therapy group to the control group. For the 26 girls in the control group, the weight change had x = -0.5 and s = 8.0. Repeat all five steps of the test of H0: μ = 0 against Ha: μ ≠ 0 for this group, and interpret the P-value.