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P-Chart: Diff. btwn lot & sample size

  1. Nov 22, 2008 #1
    Hi

    need some clearance of idea:

    A process produces rubber belts in lots of sizes 2,500. Inspection records on
    the last 20 lots reveal the following data:

    then u have data in the format:

    Lot Number non-conforming belts
    1 230
    2 235
    etc etc etc etc
    20 207

    need to calculate p-chart for it....so have p-bar = tot. defective/2500*20...right?

    what would I use as "n" to calculate the control limits?????? n is sample size so should it be 2500(lot-size here????).

    Would appreciate if anyone could clear it out for me
     
  2. jcsd
  3. Nov 22, 2008 #2

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

    If all you have is what you have given here is all you have, you don't have enough information. In particular, knowing that there were 230 defectives in the sample tells you nothing if you don't know the size of the sample. 230 defectives out of a sample of 2500 might not be too bad but 230 defectives out of a sample of 230 surely is! Are you not told how large each sample is?
     
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