Shewhart’s Control Chart: Some Observations

Abstract

Data Analysis in Shewhart’s Control Chart, to use the original m samples n sized intensities, is the main subject of this paper. Given m × n intensities we examine three alternatives to sintetize the variability: a) arithmetic mean of m standard deviations (' S); b) root mean square of m variances (" S); c) global dispersion ("" S). We prefer the global dispersion to estimate parent population σ².

As an alternative we suggest to analyze all the items of an unique random sample dimensioned in such a manner to have an efficient σ² estimate. A second introducted proposal is to use the Factory’s needs: (P ₀, P ₁, α, β, L and U). Some examples are given in the last session of the paper.