Robert Butler


  • I agree with @Straydog – the issue is that of statistics.  If we assume you have a mathematical background that includes algebra and if, for whatever reason,you can’t take a course in basic statistics then I would recommend working your way through the following books:

    1. A Cartoon Guide to Statistics – Gonick and Smith – I’ve recommended this…[Read more]

  • Things are fine on my end @cseider – hope all is well with you too.  As for the homework – it’s pretty quiet around these parts and I was feeling generous…    :-) 6 days, 16 hours ago

  • It’s just the sums of the squares of the deviation from the mean divided by the total count minus 1.

    So, for a single item the average is  (10 + 0)/2 = 5

    The deviations from the mean are

    10 – 5 = 5

    0-5 = -5

    The squares of those deviations are

    5^2 = 25

    (-5)^2 = 25

    there are two observations so  2 – 1 = 1

    Therefore the variance per item i…[Read more]

  • I’m not sure where we’re going with this discussion.  The focus of your initial post was that of coil rejection due to defects.  In the follow up discussion I was left with the impression defect reduction and thus increased acceptance of coils was your main concern.  I was also left with the impression that one factor known be a contributor to de…[Read more]

  • I’ve been giving your problem some thought and I can’t think of any single statistic that will capture consistency both with respect to stability of system variability and constancy of trending.  The issue you are facing is that of an evolution of both variation and trend across time. As far as I know, if time is involved you will have to take it…[Read more]

  • Based on your post there not only does not seem to be any need for a 1-10 rating but, it doesn’t sound like your colleague has any idea of how to build a meaningful 1-10 rating scale that would be of any value to you.

    What your post does suggest is you have some understanding of why coils are rejected.  For example, you mentioned dark surface on…[Read more]

  • The question you are asking is one of a comparison of two proportions.  Specifically you want to know if the difference between 100% and 82.5% is statistically significant for a sample of 315.

    The key is to recognize that the proportions are 315/315 and 260/315.  In other words, with a baseline of 315 in both cases we have a situation where t…[Read more]

  • The short answer to you second post is: there’s nothing like that out there.

    Let’s take another look at what you are asking:

    You said: “I was looking for some current affairs metric that can tell me if something like the historical average growth rate will continue or if a certain ratio will stay stable in the future.”

    If a measurement such as…[Read more]

  • I might be missing something but, as written, your post appears to be expressing two different requirements.  You say you want to predict variation, specifically predict variation trending, however, the examples you give have nothing to do with prediction.  Both both CD and CV are strictly summations of current affairs – they don’t have any p…[Read more]

  • ….an additional thought.  I was going over the case study and looking at the data set for Case #2 and it occurred to me that, if you want to, you can use that data set as a starting point for what would amount to an excellent self teaching exercise.

    In the attachment I’ve rearranged the data to make the composite nature of the design more…[Read more]

  • The way you would determine the minimum and maximum settings shown on page 28 would be to take the regression models for collapse and burst pressure and put them in an optimizing program and run them.  I don’t know Minitab but I do know it has such an option.

    The problem is the author has not provided the models he generated using the data.  S…[Read more]

  • I might be missing something but my understanding of the scenario you described is as follows:

    a. Quality team takes a 10% sample of the total output.  With a total output of 1000 this becomes a sample of 100.

    b. Quality team does a 100% inspection of the 100 samples and finds 10 defects in that sample.  Therefore, their claim, based on the e…[Read more]

  • If you are going to re-sample the internal audit sample then the short answer is the sample size is no longer 100 it is 110 and 11/110 = 90%. Another way to look at this is you have a sample of 100 – you find 10 defects in that sample.  You dump everything back in the bin and run a re-sample of the same population taking 10 samples and finding 1…[Read more]


    This sounds like a homework problem but I’m done with my remote work and I’m not really ready to start back in on my latest book read so…

    7 = Xbar1 = the average over 153 days.


    7 x 153 = the sum of the individual measures for the 153 day period (remember: the sum of individual measures/153 = average = 7)

    12 = the desired average…[Read more]

  • To do things like this you really need to spend the money, purchase some good books on experimental design, and read them and keep them close by as a reference.

    The two I would recommend are:

    1. Understanding Industrial Designed Experiments by Schmidt and Launsby

    2. The Design and Analysis of Industrial Experiments by Davies

    To your point -…[Read more]

  • If your question is how do you get the percentages at the bottom of the page the answer is you need information that is not present on the spreadsheet you provided. In order to get the percentages at the bottom you need to know how the efforts are apportioned to each of the consultants. The best you can do with what you have is compute total…[Read more]

  • @cseider – well, welcome back…question – your elapsed time for your most recent group of responses is 62 minutes, 57 minutes, 14 minutes, 8 minutes, and 7 minutes….what happened between 57 and 14?  Lunch break?  :-)

    Take Care

    P.S. where I work the IT department is really on the ball as far as fighting Covid is concerned.  This morning I lo…[Read more]

  • I’m not sure I understand what you mean by “statistical tools to create a baseline.”  Baseline data is just that – data gathered from a process before you attempt to make changes.  As for the data gathering itself – that is an entirely different matter.

    1. How often – I’ll take everything I can get with as much detail as I can get. This means i…[Read more]

  • In summary:

    1.    [The defects are] not deep enough emboss thickness, not enough stretching, or telescoping or collapsing rolls (and what is telescoping and collapsing – are these other ways of expressing not enough stretching or are they something else?

    2.    We know that a majority of these defects are caused by incorrect tension during…[Read more]

  • It looks like your plotting routine for the histogram is running some kind of default binning which is giving you a false impression of your data.  If you look at the linear plot of the data the histogram should have vertical bars at the same places -15, -10, -5, 0 , 5, 10, 15 but it doesn’t. Rather the histogram looks like the bars are at…[Read more]

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