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July 2001

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Subject:
From:
"Yves.Dupuis" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Tue, 3 Jul 2001 15:33:59 -0400
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Lou is right but does not suggest a number. Many people would say something
like 25. It's entirely arbitrary and no theory can tell you how many are
enough. 25 comes from the reasoning that, under most circumstances, 25
samples will make the sample s.dev. a somewhat reliable estimate of the
population s.dev. I recommend 25 in the same way that I recommend 95% as a
confidence level: no line is the best but if you insist on an arbitrary line
you could do worse than this one.

regards,
yves

Yves Dupuis
Process Engineering
Leitch Technology
Phone: 416-445-9929 X3389 / Fax: 416-445-7927
25 Dyas Road, North York, Ontario M3B 1V7

> -----Original Message-----
> From: Lou Hart [SMTP:[log in to unmask]]
> Sent: Tuesday, July 03, 2001 9:36 AM
> To:   [log in to unmask]
> Subject:      Re: [TN] Sample size in computing cpk
>
> Ken, before calculating Cpk you need to show the process is in control
> with
> SPC charts.  From the data you use to make the charts you can calculate
> Cpk.  Let me know if you need more information.  Lou Hart
>
> -----Original Message-----
> From:   Ken Fong [SMTP:[log in to unmask]]
> Sent:   Monday, July 02, 2001 10:36 PM
> To:     [log in to unmask]
> Subject:        [TN] Sample size in computing cpk
>
> Dear Technetters,
> Could anyone give some idea what the minimum sample size is when
> calculating the
> cpk of a process. And based on what theory to arrive at this minimum
> sample
> size?
>
> Thanks,
> Ken
>
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