Robert Butler


  • As written, the answer to your question is to sample 80% of the data – there’s no estimation involved.

    Sample size questions focus on moments of a distribution (things like means, standard deviations, etc.)of a sample and are phrased in the following manner: How many samples do I need to take in order to be certain that the mean/standard…[Read more]

  • @KatieBarry Ah Ha! So it IS resurrect old threads month!!!  :-)

    I’m sorry to have to admit this but I don’t think I’ve ever checked the newsletter. Thanks for the heads up. 3 months ago

  • @KatieBarry – is this resurrect old threads month?  This isn’t a complaint – just wondering. 3 months ago

  • Minitab is great so I’m sure they appreciate the 2020 tip of the hat in their direction but this thread has been dormant since 2013 so the original poster might be a bit slow in responding.  :-) 3 months, 1 week ago

  • There isn’t a simple guideline. Which one of  the design methods you use will depend on what it is that you want to do and the kinds of variables you have.

    For example:

    1. Are the variables of interest continuous (or can they be treated as continuous), are they nominal, or are they a mixture of the two?

    2. Are you trying to assess…[Read more]

  • If you have multiple responses then presumably you have a predictive equation for each of those responses.  If that is the case then you should have a minimum and a maximum level of desirability for each response.  If this is true then take your equations – put them in a program, assemble the matrix of X’s and run the equations against the m…[Read more]

  • So if I’m understanding correctly the question you are asking is how to generate a fit to the data in your plot that will be in the form of a predictive equation.

    If that’s the case then, based on just looking at the plots, my first try would be a simple linear regression using the terms pipe motion, the square of pipe motion, stiffness and the…[Read more]

  • I’m missing something.

    The idea of an experimental design is that you have little or no idea of the functional relationship (if any) between variables you believe will have an effect on the output and the level(s) of the output itself.  You put together a design which consists of a series of experimental combinations of the independent variables…[Read more]

  • Maybe we are just talking past one another but I’m not sure what you mean by “the numerical output from the process creates the shape of the model.”

    A random variable is a function that takes a defined value for every point in sample space. – Statistical Theory and Methodology in Science and Engineering – Brownlee – pp. 21.  Given this I would…[Read more]

  • Based on what you have posted the short answer to your question is – no – DOE won’t/can’t work in this situation.

    The factors in an experimental design require either the ability to change the levels of each factor independently of one another or, in the case of mixture designs, to vary ratios of the variables in the mix.  In your situation you…[Read more]

  • I’m not sure what you mean by the regular rules.  If you mean the issue of control limits based on standard deviations about the means then you can still use them.  The issue is one of expressing the data in a form that will allow you to do this.  When you have an absolute lower bound which is 0 the usual practice is to add a tiny increment to th…[Read more]

  • That would make sense if the aspect of the supplements you believe most impacts the outcome is the percentage of total nitrogen, otherwise it won’t matter.

    The idea is if total nitrogen was understood to be the critical component of the supplements you would chose the two supplements with the lowest and highest levels of total nitrogen and run…[Read more]

  • If you have a situation where you can only run one raw material with no combinations of other raw materials and similarly for the catalysts and the supplements and you have no underlying variables that would allow you to convert them the continuous measures then you are stuck with running all the possible combinations which would be 480.  I…[Read more]

  • You will have to provide some more information before anyone can offer much of anything in the way of advice.  You said, “I have 15 difference raw materials (A1, A2… A15), 4 catalysts (C1, C2, C3, C4) and 8 supplements (B1, B2…B8). ”


    1. Is this a situation where the final process can have combinations of raw materials, catalysts and…[Read more]

  • The short answer is the CLT doesn’t have anything to do with the capability analysis.

    You are correct – the CLT refers to distributions of means not to the distribution of any kind of single samples from anything.  The statement from the WI (whatever that is)  “based on the CLT, a minimum sample size of n ≥ 30 (randomly and independently sam…[Read more]

  • Control charts don’t test for normal distribution and, while the standard calculation for process capability requires approximately normal data, it is also true that process capability can be determined for systems where the natural underlying distribution of the data is non-normal.  Chapter 8 in Bothe’s book Measuring Process Capability titled…[Read more]

  • @andy-parr  it’s a spammer.  They get through from time to time – I’ve had the same person/entity trying for the same thing.  I’ve seen a few in the past as well.  This one is just more persistent. 5 months, 2 weeks ago

  • From what I found after a quick Google search for the definition of TMV the big issue with that process is exactly what you stated in your second post: TMV focuses on the issue of repeatability and reproducibility.  Since assessment of repeatability and reproducibility are the main issue and since it was what I thought you were asking in your…[Read more]

  • After a Google search I’m guessing that TMV stands for Test Method Validation.  If this is the case then I think you need to back up and re-think you situation.

    What follows is a very long winded discourse concerning your problem so, first things first. The short answer to your question is – no – running a TMV and pretending the bi-modal nature…[Read more]

  • I would disagree with respect to your view of a histogram for delivery time.  I would insist it is just what you need to start thinking about ways to address your problem.

    Given: Based on your post – just-in-time (JIT) for everything is a non-starter.

    Under these circumstances the issue becomes one of minimization of the time spread for late…[Read more]

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