# A question for Reigle Stewart

Six Sigma – iSixSigma Forums Old Forums General A question for Reigle Stewart

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• #35228

Dr. Steve W.
Participant

Mr. Stewart,
Since you know Dr. harry so well, you might know the answer to this question: how was the sample size formula (given delta, SD, alpha and power level) derived? It does not give the same answer Minitab gives (My understanding is that Minitab uses iterative algorithm to solve for sample size). I did some search but did not find anything that helps me understand the formula was derived. If you could shed some light, I would appreciate it greatly.

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#98517

Reigle Stewart
Participant

Dr Steve W: You may recall a book by Dr. William
sample size (equal variances, group comparison). The
equation is: N1 = N2 = 2(Z.a + Z.b)^2 * V / D^2. Once this
equation is computed, the computed N is used to find the
values of t.a and t.b (t distribution) during the second
computation. So, we have a single iteration of the
equation that is used to find the second solution. If this
does not match the Minitab output, I don’t know what to
say. Perhaps call Minitab or maybe Dr. Terry Zimmer
knows (former Minitab statitician). Reigle Stewart

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#98580

Disappointed
Participant

Based on previous posts, Dr. Steve W should know the answer to this one.  What happened?  Has Stan’s insults hurt your self esteem?  And all Reigle did was to reiterate the formula rather than provide any new insight.  Bring back the Shroeder thread, at least we were learning something.

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