What is the minimum of sample size per subgroup to create a P-chart?

[bhr-q]

  Hi everyone,

Hi everyone,

I've created a p-chart to monitor a binary variable on a quarterly basis. But I noticed a p-chart requires at least 20 data points. So, I've shifted to monthly reporting.

with this adjustment I have reduction in the # of obs per subgroup when moving from quarterly to monthly charts.

Could you please see the attached file and advise if the sample sizes per subgroup are adequate for generating a reliable p-chart?

Thank you!

[ballardw]

Are you asking how to make a chart in Excel? All I can see is screen shot of an Excel spreadsheet which doesn't tell me anything about how any graph is made.

If that is SAS output then show how you generate it in SAS, at least the code.

[bhr-q]

I used SAS not excel, I just reported in Excel. I don't have problem with SAS at this time,
I just asked my question here as I noticed some people worked with SPC chart and I hope to help me

[ballardw]

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@bhr-q wrote:
I used SAS not excel, I just reported in Excel. I don't have problem with SAS at this time,
I just asked my question here as I noticed some people worked with SPC chart and I hope to help me

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If you share your SAS code, if not your data or Log (hint), then you may get a better answer to your question. The options chosen for any procedure effect output.

[bhr-q]

I used the below code, but I am fine with the code, as you see in screen shot I created the p chart both monthly and quarterly(no error or warning) in SAS , just to be sure I want to know what is the min number per subgroup to be eligible to use P chart?
proc shewhart data=tmp21;
pchart yes_answer*month/Markers subgroupn = total_count ODSTITLE="P-chart of Pts with IV Set"
outtable = tmp21table
nohlabel TURNHLABELS;
LABEL yes_answer ="Prop of Pts with IV Set";
run;