RE: Attribute charts - sample size

[tpr@po.cwru.edu (Tom Ryan)]

I have written extensively about the use of attributes charts, but
I have never written a paper with Heinman. I did not care for the 
approach that Heinman advocated in his article, so naturally I do not 
want my name associated with it (as Alson Look did in his post).

Harry did state on page 191 of his (1986) book that an individuals
chart could be used for attributes data if the sample size is so
large that a p-chart will have more sensitivity than is necessary.  

Tom Ryan


>Harrison Wadsworth in his book Modern Methods for Quality Control and
>Improvement (1990?) mentions using individuals control charts for attribute
>data.  I had the opportunity to talk to him about this.  He did not specify
>any particular number but seem to indicate in the thousands.  More recently
>there was a paper in Journal of Quality Technology a few years(?) ago that
>might help.  I can't remember the exact title and authors sorry.  I believe
>it was something to the effect of attributes control charts and the authors
>were Heinman and Ryan.  I did scanned the article.  It seemed that a sample
>size in the high 400s was the point in which one should switch over to an
>individuals control chart.
>
>Alson C H Look
>Sr Engineer
>alson.look@e-tek.com
>Standard disclaimers. 
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