|Author||Topic: Standard Deviation question|
|On a recent college exam, I encountered a question about Upper and Lower Control limits. The question requires finding the upper and lower control limits using the following information:
z = 2.5, n = 4, "The process has a known standard deviation of 3 and a mean of 15."
So, is the UCL/LCL = 15 +/- (2.5*3); or is the UCL/LCL = 15 +/- (2.5*1.5) (the 1.5 comes from 3/(SQRT(4))).
The question comes down to whether the standard deviation is population or sample. What do you think?
|what is your alpha level?
it looks to me since you are using a z distribution instead of a t distribution and standard deviation is known, you should be using a population stdev, right????