X-bar and s Charts - NCSS

c E s= s 4 The calculation of E(s) requires the knowledge of the underlying distribution of the x ij’s. Making the assumption that the x ij’s follow the normal distribution with constant mean and variance, the values for c 4 are obtained from c n n 4 2 1 1 2 = − − Γ Γ Estimating Sigma – Weighted Approach

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