Robert Butler


  • The yes/no is the X variable and the  percentage is the Y  therefore just code no = -1 and yes = 1 and regress the percentage against those two values.  As for the p-value the “traditional” choice for significance of a p-value is < .05 so, using that criteria a p of .127 says you don’t have a significant correlation between the yes/no and the pe…[Read more]

  • There’s any number of ways you could do this.  You could run a regression with percentage as the Y and yes/no as the X.  You could use a two-sample t-test with the percentages corresponding to a “no” as one group and the percentages corresponding to a “yes” as the other group.  If the distribution of the percentages is crazy non-normal you mi…[Read more]

  • The short answer to your question is there isn’t a short answer to your question.  The explanation provided by Wikipedia is a good starting place but you will have to take some time to not only carefully read and understand what is being said but also put pencil to paper and work through some math.

    I’ve spent most of my professional career as an…[Read more]

  • The phrasing of several of the questions is terrible…and there is one that is simply wrong.  Now that we have that out of the way my thoughts on the questions are as follows:

    Question 46: I would choose B.  When you lay a t-square over the plot there is no way the minimum at 6 is anywhere near 100. If they are claiming D is the correct answer the…[Read more]

  • The question you are asking is one of binary proportions. Since you have a sample probability for failure (p = r/n where r = number of failures and n = total number of trials) in the one environment you also have a measure of the standard deviation of that proportion  = sqrt([p*(1-p)]/n).  You also have a measure of the proportion of failures in a…[Read more]

  • @cseider – …could be… Happy New Year to you too.   :-) 6 months, 2 weeks ago

  • The original focus of this exchange was the issue of the validity of the underpinnings of the T-chart.  Your conjecture is that you have developed a theory and this theory is correct and the, apparently to you, unknown theory behind the T-chart is wrong.  Your approach to “proving” this is to

    1. Ask for a bunch of MBB’s to provide a solution to p…[Read more]

  • Oh well, in for a penny in for a pound.

    @fausto.galetto – great – so now you have completely contradicted your denial of the comments I made in my first post.

    I said the following:


    1. A quick look at the file you have attached strongly suggests you are trying to market your consulting services – this is a violation of the TOS of this s…[Read more]

  • What an IMPRESSIVE retort!!!  @fausto.galetto DO YOU appreciate the INEFFABLE TWADDLE of this entire thread (see, I can yell, insult, and boldface type too) ?

    Let’s do a recap:

    1. OP initial post says he wants a solution for two items in an attached document.

    2. I do a quick skim and offer the comment that I think the correct venue for the OP…[Read more]

  • To answer your question:

    There are two equations one for alpha and one for beta.

    What you need to define is what constitutes a critical difference between any two populations (max value, min value)

    What you have is the sample size per population (8) and for the conditions you have specified you have -1.645 (for the alpha = .05) and +1.282 ( for…[Read more]

  • your post is confusing.  What I think you are saying is the following:

    You have 13 groups and each group has 8 samples.

    The data is non-normal

    You checked the data using box-plots and didn’t see any outliers

    You chose the Kruskal-Wallis test because you had more than 2 groups to compare.

    You ran this test and found a significant p-value.

    If…[Read more]

  • I agree nobody, including yourself, tried to solve the cases.  As I’m sure others will tell you, the usual procedure on this site is for you to try to solve the problem, post a reasonable summary of your efforts on a thread and then ask for help/suggestions.

    @Darth pointed you in a direction and gave you a reference.  Given what he offered your a…[Read more]

  • Based on your post it sounds like you have no idea where your process is or what to expect.  If that is the case then the first thing to do is just run some samples and see what you see – how many to run will be a function of the time/money/effort you are permitted to use for what will amount to a pilot study whose sole purpose will be to let you…[Read more]


    During the time I provided statistical support to R&D groups my method of support went something like this:

    1. Have the researchers fill me in on what they were trying to do.

    2. Walk me through their initial efforts with respect to quick checks of concepts, ideas – this would usually include the description of the  problem as  well as p…[Read more]

  • A quick Google search indicates push, pull, and conwip are all variations on a theme – basically they focus on having work in progress throughout the line (CONWIP = Constant Work in Progress).  The same Google search indicates line balancing is just the practice of dividing the production line tasks into what are called equal portions with the id…[Read more]

  • All of the cases of which I’m aware of that have run simulations of the results of an experimental design have had actual response measurements from which to extrapolate.  If the simulation is not grounded in fact then all your simulation is going to be is some very expensive science fiction.

    A few questions/observations and an approach to as…[Read more]

  • 1. A quick look at the file you have attached strongly suggests you are trying to market your consulting services – this is a violation of the TOS of this site.

    2. If you want to challenge the authors of the books/papers you have cited, the proper approach would be for you to submit your efforts to a peer reviewed journal specializing in…[Read more]

  • I think you will need to provide more information before anyone can offer much in the way of suggestions.

    1. You said, “The data we have received are sales numbers of 2016-2017-2018 accompanied with purchase number and of course the Sales price and purchase price.”

    2. You also said, “We have to come up with a demand -forecasting model + re-order…[Read more]

  • In re-reading your comments it occurred to me there is an often overlooked but critical aspect to the issue of variable assessment using the methods of experimental design which should be mentioned.

    In my experience, the worry that one might miss an important interaction when making choices concerning experiments to be included in a design is…[Read more]

  • I’m not trying to be mean spirited or snarky but it’s called “experimental” design and not “infallible” design for a reason.  :-) Seriously, this is a standard problem and one every engineer/scientist/MD faces.  Your choices of variables to examine are, of necessity, based on what you know or think you know about a process and the number of e…[Read more]

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