Question

You are hired by a pharmaceutical company to determine if a multi-vitamin they developed can reduce the number of days the average person is sick each year. Stats Canada reports that the average number of days a person is sick each year is 18.7 (St Dev = 10). You select a sample of 40 people and given them a multi-vitamin each day and record the number of days they are ill for the next year. They are sick an average of 16.1 days (St Dev = 8). The result was not significant, but the company wants you to try the experiment again. Assuming the data above represents the actual change in number of sick days after taking the multi-vitamin, how many people would have to test to achieve a power of .80?

Answer 1