Power and sample size

Assessment

Adjust the variables and then draw the curves until you find the value of n which produces a test with 90% power

You are planning a new health promotion strategy to increase the consumption of fresh fruit and vegetables in your population. One of the outcomes you hope to observe is a reduction in the mean level of cholesterol of 0.2 mmol/L. ( - the difference between the two means)

You intend to conduct two surveys to measure the effect of your health promotion strategy, one survey before the health promotion strategy is implemented and one in two years time. (the two curves)

Assume the standard deviation of serum cholesterol levels in the general population is 1.0 mmol/L (). The significance level is 5%. ()

Set the correct values for , and and then adjust n until you find the number of people you would have to measure to have exactly 90% power to detect a difference of 0.2 mmol/L .