# Robert Butler

## Activity

• Is there any way of getting this done? – Yes, start over because, based on your description of what you are doing, you are a very long way from being able to make any kind of decisions concerning employee performance.

Let’s do a recap of your initial post.

1. You said,”We convert the survey responses into continuous data (ex.: Liker scale 1 to…[Read more]

• My guess would be your friend did something wrong in Minitab. If you don’t have subgroups then there is no within to use for calculations. Is there any chance the standard deviation it did compute was either just the sample standard deviation of all 60 points or the standard deviation of the mean of the 60 data points? 3 months ago

• A Google search will provide you with what you need.

Here’s one I found for Cpk

• When you say you “have a lot of Attribute data for my analysis (Pass/Fail)” there isn’t much anyone can offer because that statement doesn’t tell anyone what you mean by “a lot.”

However, if we make the following assumptions:
1. You take grab samples of a given size from your production process and you inspect each item in the sample…[Read more]

• Addendum – I played around with the data you posted and I must admit I don’t see how Minitab generated those estimates. The average of the non-missing data is -14.1 and the standard deviation of the non-missing data is 90.9 which means your 2 sigma limits would be (upper) = -14.1 +2*90.9 = 167.7 and the lower would be -195.9.

• A missing value is a missing value – what you have done is construct an entirely different set of data with a lot of average values in place of the original missing values. Under these circumstances you should expect to get something different because the two data sets are not equivalent.

I don’t have Minitab but my guess is that Minitab is…[Read more]

• As written, your post doesn’t provide enough information concerning your objective. My guess is that you are looking for tester agreement when running tests on split samples but maybe not. If you are looking for agreement then that is not the same thing as correlation and you will need more than a simple check of correlation to determine…[Read more]

• It looks like excel is just computing the standard deviation of the sample and then giving you the plus/minus 2 standard deviations of the sample whereas Minitab looks like it is computing USL and LSL spec limits 4 months, 2 weeks ago

• @Darth – things are going well here – how about you and yours? 4 months, 2 weeks ago

• Given what you have posted, I think you are faced with one of two scenarios.

(In order to provide some clarity with respect to what follows let’s pretend the treatment has as part of its application changes in temperature and pressure. Given this then there are at least two different versions of “no treatment”.)

1. The situation for “no…[Read more]

• Darth is correct. Here’s the relevant quote from a standard statistics text.

Applied Regression Analysis 2nd Edition – Draper and Smith pages 22 and 23

“[with regard to regression] Up to this point we have made no assumptions at all that involve probability distributions. A number of specified algebraic calculations have been made and tha…[Read more]

• As for the second link the following commentary from their site

“Consider the two regression models, and their residuals plots, shown here:

The (lower) plots show the residuals for each model (the residuals are the errors between the regression lines and the actual data points). It can be seen that:

1) The residuals for the ‘good’ reg…[Read more]

• Well, the best I can tell you is what I said in my first post – most of what you quoted is wrong.

Specifically – to the points made on the first site:

“There are four assumptions associated with a linear regression model:”

“Linearity: The relationship between X and the mean of Y is linear. ”

Not true – see the reference I gave in the…[Read more]

• It occurred to me your phrase “Homoscedasticity: The variance of residual is the same for any value of X.” could be interpreted as a short verbal summary of the paragraph I wrote concerning what to look for when running the residual analysis. If this is the case then the statement is true but I think it is far too brief and could easily mislead…[Read more]

• I’m afraid most of what you have stated is wrong.

My reference is Applied Regression Analysis 2nd Edition – Draper and Smith

1. There are no restrictions on the distributions for either the X or the Y. The question of normality (or approximate normality) is one that is restricted to just the residuals.

The variance of the residuals is…[Read more]

• I guess my first question would be – where did you get a KPI of 120 books/hour? That amounts to a minimum of 1 book every 30 seconds.

Given your description “The rate is picking 120 units (books) per hour. They use carts, and are guided through the warehouse using tablets. What are some barriers that I should be looking for?” My personal…[Read more]

• No, the variability identified by your SPC chart is the ordinary variation of your process. If you try to use control limits that have nothing to do with your process all you will do is add to the process variation and make everything worse – this is known as over control.

Usually a reference material is some kind of gold standard and you use…[Read more]

• Because, the contrast (or contrasts) that make the AxB interaction significant may not be the set of contrasts tested by just focusing on comparisons with a control.

As for your recommendation – if your design matrix is such that the 0 setting for either A or B really means a complete absence of either A or B and not a case of A or B being at…[Read more]

• No, the two methods do not show different results – the issue is you are not making the proper comparisons.

In the regression you found the AxB interaction to be significant.

In the test for group differences you chose to run a comparison against the control – this isn’t what you want to do.

There are 4 combinations that comprise the AxB…[Read more]

• I was looking at your data set again this evening and it occurred to me if you look at the data for count and count2 there is major difference between the two columns.  If count and count2 represent the results of a design and a full replication (I doubt this since the total counts are the same for both count and count2 but bear with me) of the 2…[Read more]