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Normality Tests

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  • #50715

    Priyanku Nandi
    Participant

    Hi,
       I have  6 months data and wish to know would it be necessary to perform normality tests on this data in order to form baselines.
    Can I use X bar charts and R Charts ?
    Thanks

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    #174740

    Bob H
    Participant

    Normality is not a requirement for X-Bar & R, but at times significant non-normality (bi-modals, heavy skewing, etc.) can cause some SPC test failiures.
    If you want to run a capability analysis (I’m assumign you have variable data here), you need to run both normality and stability tests first.  You need the normality test to insure you are applying the correct capability model, and you need stability to make sure that you’re not chasing a moving target…

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    #174743

    annon
    Participant

    Bob H is on point….Once you have your data, run a 4S (for continuous data) – Stability, Shape, Spread, Senter….this will tell you what you need to know when selecting the proper capability metric for baselining your process….So control chart/run chart, histogram/AndersonDarling test, variance/std dev and mean (you can pull these off your xbar charts)…..
    Good luck.

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