iSixSigma

p chart

Activity

  • p chart replied to the topic P-Charts w/LARGE Sample Sizes in the forum General 15 years ago

    are the charts truly used to monitor the process? if they are historical data being reviewed for trending, then the run chart is the appropriate tool because the chart is not being used for process control. in this case the control limits are superfluous because you will not react upon them.

  • p chart replied to the topic P-Charts w/LARGE Sample Sizes in the forum General 15 years ago

    yes, you’ve run into a ceiling problem. Convert to an IMR chart by charting the proportions as individual values, and see what happens. If that doesn’t work, use a simple run chart. You’ll still find clustering, mixtures etc.

  • p chart replied to the topic P-chart in the forum General 15 years, 5 months ago

    Charles,
    What I find interesting is the fact that in most MBA and PhD programs Six Sigma plays a very minor role. By contrast quality and systems theory are very well represented and alive in operations management classes. In general business administration education has moved away from integrating fields such as operations management,…[Read more]

  • p chart replied to the topic P-chart in the forum General 15 years, 5 months ago

    Charles,
    You are absolutely correct … I guess, eventually, we all get sucked into the CNN sound bits of the “general business literature” and recite the slogans that we have heard over and over and over again … until they finally become the eternal and unquestionable truth. Deming would not have been amused :-). Thanks for the reminder.

  • p chart replied to the topic P-chart in the forum General 15 years, 5 months ago

    As always, there is little to argue with the dark side’s black and white summary of basic facts. There are two things that I think should be added to the list of the basics of control chart.
    1. The control chart was developed under the assumption of sampling. Thus the limits are both a function of the proportion defefective and the total sample[Read more]

  • p chart replied to the topic OUT OF CONTROL : DOUBT in the forum General 15 years, 5 months ago

    It is absolutely amusing to see a rude and unprofessional response go up in the flames of its own ignorance: factually, there is a difference between a subgroup and a rational subgroup, and the term subgroup is used for both attribute and variable charts. Rational subgrouping, on the other hand, is used only in the context of variable charts. And…[Read more]

  • p chart replied to the topic OUT OF CONTROL : DOUBT in the forum General 15 years, 5 months ago

    What is your total sample size per month? You may get these types of erratic out-of-control points simply because you are throwing very large datasets into your SPC package. As a result your control limits will shrink and you’ll run into the type of problem you are describing. Control charts are designed for the active review of processes not the…[Read more]