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Optimal samples in Individuals Charts

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  • #32588

    Pomara
    Member

    Dear All
            I am confronted with the task of determing the optimal number of smaples to take (to get reliable control limits) for an Individuals Charts.
    Not sure how to proceed with coming up with a recommendation. I have historical data to play around with (i.e. expect the cv’s of the material to be plotted to be in the range b/w 2 to 5 %).
    Sugestions welcome on the way forward.
    regards
     
     

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    #87187

    marklamfu
    Participant

    For getting a reliable control limit of X_bar chart, generally, number of subgroups is 20 at least , each subgroup include a few samples ( >3), total samples 60~100, for individual chart, every subgroup only have 1 sample, considering the nature of normal distribution, 30 samples is recommended.

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