Hi everyone,
I want to Apply Tests for Special Causes in p-chart, but the sample size for each group is different. So I don’t have a fixed UCL and LCL. Just a question can I apply Tests for Special Causes? Can I calculate index when I don’t have a fixed LCL and UCL.
Thanks,
Thank you for your answer. Just a question: Since each subgroup has a different sample size, there would be different probabilities, and different UCL and LCL, as you have in your example.
but I can see you get the fixed number for UCL and LCL at the top of your example: UCL: 10.97301
LCL: -0.76276
how do you get the fixed number for them?
my example is like a different sample size for each group and I am looking to have a fixed UCL and LCL for them to get the plot.
Thanks,
Bahar
This is the raw data. Please understand it according to the P diagram method
Product P chart for non-conforming products within one month, one sample will be taken every day within one month
Samples were taken and the number of non-conforming products was checked, with a total of 26 days of data collected.
The data is as follows:
Inspection quantity Unqualified quantity (nP)
158 11
140 11
140 8
155 6
160 4
144 7
139 10
151 11
163 9
148 5
150 2
153 7
149 7
145 8
160 6
165 15
136 18
153 10
150 9
148 5
135 0
165 12
143 10
138 8
144 14
161 20
Hi Yanping,
I have a question regarding theP-chart. I created a P-chart for one binary variable. Attached is the screenshot of that; as you see, I am interested in monitoring improvement quarterly, but as I have a cohort for two years, there are only 8 data points/ 8 quarters; I was just wondering if this plot is acceptable?
Thank you!
Thank you for your answer,
I did the same as you, except that there are only 8 data points in my plot because I consider monitoring by quarter; I have a concern about considering by quarter.
I think it would be better to consider by month, not by quarter; this way, I have more data points.
Is that right to say the number of data points in the p-chart should be at least 20?
In my case, as you see in the plot the number of points is 8
If I consider by month, then the number of sample sizes is like below, is it possible to create p-chart for this sample size? what is the minimum number for each subscale to crate p-chart?
202108 12
202109 19
202110 20
202111 24
202112 24
202201 20
202202 24
202203 12
202204 15
202205 23
202206 30
202207 20
202208 24
202209 27
202210 21
202211 32
202212 23
202301 24
202302 26
202303 35
202304 27
202305 33
202306 38
Thank you
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 number 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?
what is the minimum required number of obs per subgroup to use a p-chart effectively?
Thank you!
Thank you!
The data includes the number of inspected samples and the percentage of unqualified samples
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