A study is performed to estimate the mean change in serum cholesterol among patients given who start on statins. Let change stand for the parameter of scientific interest. To estimate change we plan to collect data from 16 patients. Let X1, X2, ...X16 be the changes in cholesterol experienced by these patients and stand for the average of these values that we will calculate.

The standard deviation of the change in cholesterol is 20 mg/dl. What is the standard error of x?

a)5

b)20

c)1

d) unknown