Frank Grinder is trying to introduce sampling into the quality control program of an old-line manufacturer. Currently, each item is individually inspected to make sure it meets size tolerances. For all items manufactured during August, the standard deviation of size was 0.02 centimeters. If Grinder takes a sample of 30 items and finds a standard deviation of size of 0.019 centimeters, what is the standard error of the sample mean?
If we know the standard deviation of the population (in this case we do), then the standard error of the sample mean = the standard deviation of the population / the square root of the sample size = 0.02 / √30 = 0.00365 centimeters. | 
发表于 2010-4-16 08:30
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