As far as I know, there is no such thing as a standard deviation for a "group" of one item. I can talk about the standard deviation of individuals within the population, but not a subgroup of one.
If I understand the request correctly the within subgroup standard deviation is estimated using the moving range....
SD = average moving range / d2 where d2 is 1.182 (subgroup size' n=2)
If I understand the request correctly the within subgroup standard deviation is estimated using the moving range....
SD = average moving range / d2 where d2 is 1.182 (subgroup size' n=2)
Yes, my confusion or doubt comes from the Minitab software documentation.
Minitab:
"Estimating σWithin when subgroup size = 1
Average moving range ? Default
Withinσ?= StDev(Within) = ()wdRM2
MRi = the ith moving range = max[xi, ?, xi-w+1] ? min[xi, ?, xi-w+1], for i = w, ?, n RM= ()()1...+−++wnMRMRnw
w = the number of observations used in the moving range. w = 2 by default."
However I have managed to solve my problem. Thank you for your comments and assistance and sorry for my English.