Example of P Chart with unequal subgroup sizes
main topic     interpreting results     session command     see also 

Suppose you work in a plant that manufactures picture tubes for televisions. For each lot, you pull some of the tubes and do a visual inspection. If a tube has scratches on the inside, you reject it. If a lot has too many rejects, you do a 100% inspection on that lot. A P chart can define when you need to inspect the whole lot.

1    Open the worksheet EXH_QC.MTW.

2    Choose Stat > Control Charts >Attributes Charts > P.

3    In Variables, enter Rejects.

4    In Subgroup sizes, enter Sampled. Click OK.

Session window output

P Chart of Rejects

 

 

 

Test Results for P Chart of Rejects

 

 

TEST 1. One point more than 3.00 standard deviations from center line.

Test Failed at points:  6

 

* WARNING * If graph is updated with new data, the results above may no

          * longer be correct.

Graph window output

 

 

Interpreting the results

Sample 6 is outside the upper control limit. Consider inspecting the lot.