Neil Polhemus

Interaction effects are typically not calculated in a randomized block design, because blocking factors and experimental factors are usually assumed not to interact. Further, unless there is replication, there will be no degrees of freedom available to estimate the experimental error if you do estimate the interactions. However, you may estimate…[Read more]

I don’t think you’d ever want to stop collecting data and plotting it on a routine basis. You can always learn from looking at your data. You’d also like the ability to detect changes before they cause a problem, and that’s what control charts are designed for.You might consider modifying the control limits, however, to allow for the wide…[Read more]

Good point. A special toolwear chart does have a couple advantages, however. (1) You can specify the slope of the line if desired, rather than estimating it from the data. (2) You can add a specification limit to the plot to tell when you are getting close to needing to change the tool.

There are control charts specifically designed to monitor tool wear. STATGRAPHICS contains one such chart designed to handle wear which follows a linear trend.

Now that’s an intriguing question. If someone screws up, is that part of the measurement process? It may be.

I did some experimenting, and outliers actually seem to have a bigger impact on the ANOVA method than the Average and Range method (much bigger in the examples I tried).

The MSA manual recommends the use of the ANOVA method unless a computer is not available. One possible explanation for a dramatic difference between the results of the 2 methods is the optional inclusion of an appraiser by part interaction in the R&R term estimated by the ANOVA method. It would be surprising to see a large difference between the…[Read more]

Before embarking on any SPC or DOE effort, you must be certain that you are capable of measuring the characteristics which are critical to your process. If you can’t measure those characteristics accurately and precisely, then you won’t be able to distinguish good parts from bad parts or be able to determine the effect of any changes you might…[Read more]

You can send it to me at P.O. Box 1124, Englewood Cliffs, N.J. 07632, or e-mail a file to [email protected]

I also second the idea of putting the e-mail addresses back.

I ran it through the Automatic Forecasting procedure in STATGRAPHICS. On the limited amount of data you provided, the winning method was a simple random walk: the forecast for next month equals this month’s amounts. If you provide more history, it is possible that we could do better.

What we are concerned about with gage linearity is that the measurements from a gage should increase linearly with the response or, if a gage is biased, the bias should remain constant over the range of measurements for which that gage is used. While we can tolerate a little non-linearity, it should be small with respect to the normal process…[Read more]

That’s very interesting. Can you tell us how you set up the model for GLM? It’s not clear to me how you would do that.

I second Terry Harris’ suggestions. Anything beyond a two-level factorial makes no sense for the yes/no input factors. It might be simpler to go with a modified Box-Behnken design where you split the centerpoints amongst the levels of the attribute factors. I would not just go in and adjust the star points in the CCD. The resulting design will be…[Read more]

If you can collect a lot of samples at each combination of the factors, then you can use the proportion of failures as the response. You could then do a logistic regression. However, you may be able to use a standard ANOVA approach with an arc sine square root transformation (Box, Hunter and Hunter discuss this approach on p. 134). If you are…[Read more]

You can sample the world with 10? An election poll with 10 respondents? A sample of 10 items from a lot of 10,000? Not my world.

If the data is balanced, as it appears to be (2 replicates at each of the 12 factor combinations), then I suggest you check your arithmetic. The factor and interaction sums of squares must add to less than the total and the error sum of squares can’t be negative.

In Version 5 of STATGRAPHICS Plus, we added the capability to link a StatFolio (our basic document) to various data sources, including Excel. You can set the program to poll the Excel file at regular intervals and automatically update any charts you have created. These charts can also be automatically posted to a web server whenever they are…[Read more]

The basic principle of controlling to a standard is certainly sound, and solving backwards for the required sigma is commonly done. You might also check out the discussion of Acceptance Control Charts in Doug Montgomery’s book “Introduction to Statistical Quality Control”, where he works the specs into the establishment of the control limits from…[Read more]

It is important not to confuse the concept of capability with that of control. The control limits do not provide your estimate of process capability. That comes directly from the mean DPU. The control limits simply allow you to determine whether the process has been stable over the sampling period.