A crossover trial is conducted to compare an experimental me

A crossover trial is conducted to compare an experimental medication for migraine headaches to a currently available medication. A total of 50 patients are enrolled in the study and each participant receives both treatments. The outcome is the time, in minutes, until the headache pain resolves. Following each treatment, patients record the time it takes until pain is resolved. Treatments are assigned in random order. The mean difference in times between the experimental and currently available medication is -9.4 minutes with a standard deviation of 2.8 minutes. Construct a 95% CI for the mean difference in times between the experimental and currently available medication.

Solution

z-score at 95% = 1.96

confidence interval = mean +/- z-score * standarddeviation/sqrt(size of sample)

=>

confidence inetrval = -9.4 +/- 1.96 * 2.8/sqrt(50)

= -9.4 +/- 0.7761

= (-8.62 , -10.18)