1. A crossover trial is conducted to compare and experimental medication for mig

Question

1. A crossover trial is conducted to compare and experimental medication for migraine headaches to a currently available medication. A total of 50 patients are enrolled in the study and each patient received both treatments. The outcome is the time, in minutes, until the headache pain resolved. Following each treatment, patient’s 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.

2. Suppose in the study described in Problem above each patient was also asked if the assigned medication caused any stomach upset. Among the 50 patients, 12 reported stomach upset with the experimental medication. Construct a 90% CI for the proportion of patients who experience stomach upset with the experimental medication.

Explanation / Answer

(1) Given n=50, mean difference=-9.4, s=2.8
a=0.05, Z(0.025)=1.96(check standard normal table)

So 95% CI is
-9.4 ± 1.96*2.8/50

--> (-10.18, -8.62)

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(2) Given n=50, p=12/50 = 0.24

Given a=0.1, Z(0.05)=1.645(check standard normal table)

SO 90% CI is

p ± Z*[p*(1-p)/n]

--> 0.24 ± 1.645*sqrt(0.24*(1-0.24)/50)

--> ( 0.14, 0.34)

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