Minimum number of Subgroups to assess Process Capability

D

DJN

What is considered to be the minimum number of subgroups to assess process capability? I have been using 20 but have now been informed that 25 should be used. Is this correct?
 
M

M Greenaway

The QS9000 SPC manual generally recommends at least 25 sub-groups.
 
D

D.Scott

Hi David - welcome to the Cove.

An automotive PPAP using an X-bar and R chart would require a minimum of 25 subgroups containing at least 100 consecutive samples.

Dave
 
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