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Protection offered by the sampling plan

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  • #44211

    Anand
    Participant

    For the OC curve, I have been given the AQL and LTPD values, how do I describe the protection offered by the sampling plan at these quality levels?
    For the data given below:
    Sampling type = Single SamplingLot size = 1500Sample size = 150Acceptance no. = 3. AQL = 0.05%LTPD = 6%

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    #141346

    Mikel
    Member

    That AQL is not accurate

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    #141348

    Mikel
    Member

    This would be more accurately described as an AQL of about 1% and LTPD of about 4%.

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    #141351

    Six Sigma Tom
    Member

    I suggest that you plot the entire OC curve and look at it. The OC curve IS the description of the “protection” provided by the plan to both the producer and the consumer. The ideal OC curve looks like a Z. It is nearly 1.0 at the AQL or better quality and nearly 0.0 at the LTPD or worse quality. The key word here is “nearly.” Usually the producer (supplier) tries for a high probability of acceptance at the AQL (e.g., 90%+, the higher the better.) Consumers want a low probability of acceptance (10% or less, the lower the better) at the LTPD. The constraint is the cost of sampling. To approach a “Z” shaped OC curve you have to spend more money on sampling.

    Normally, back in the days when acceptance sampling was widely used, the contract would just stipulate that a standard be used (nearly always Mil-Std-105D or, later, Mil-Std-105E or one of the ANSI/ASQC equivalents.) and the AQL or LTPD specified.

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