Chapter 12, Problem 18SE

A Smile a Day Smiling is a sign of a good mood, but can smiling improve a bad mood? Researchers plan to assign subjects to two groups. Subjects in both groups will rate their mood at the beginning of the study. Then subjects in the treatment group will be told to smile while they are asked to recount a pleasant memory. Subjects in the control group will also be asked to recount a pleas-ant memory, but they will not be told to smile. Both groups will again rate their moods, and researchers will determine whether the reported moods differ between the two groups. Because the initial, baseline mood rating might affect the outcome, after the first mood rating the subjects will be broken into two groups: one group with low ratings (“bad mood”) and one with higher ratings (“good mood”). Patients in each group will then be randomly assigned to either the treatment group or the control group. Is this an appropriate use of blocking? If so, explain why. If not, describe a better blocking plan.