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AUS-DOH-Safety-and-Quality / PowerBI-SPC

A free and open-source PowerBI custom visual for SPC charts
GNU General Public License v3.0
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show dates with zero data points #311

Open boyddt opened 3 months ago

boyddt commented 3 months ago

hello, so far I like what I see but have a few questions. How are the UCL and LCL calculated. we use + or -3 sigma and comparing your output to Minitab show a slight variation. 5.66 for your app and 6.759 from Minitab. Second, for months where this no data, is there a way for the chart to show those months. The screenshot below shows that it skipped March 2024.

Thank you for this excellent tool

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andrjohns commented 3 months ago

Great to hear that it could be useful!

How are the UCL and LCL calculated. we use + or -3 sigma and comparing your output to Minitab show a slight variation. 5.66 for your app and 6.759 from Minitab.

The formulas for each chart type are listed here in our documentation, and you can find the code used for each type in this folder of the repo

Feel free to get in touch if there's a particular discrepancy or anything that I can clarify.

Second, for months where this no data, is there a way for the chart to show those months. The screenshot below shows that it skipped March 2024.

Ah good question. Not currently no, as the data is being filtered during pre-processing so that months with all null values are removed. The request has come up before, so I can add it to the to-do list

andrjohns commented 3 months ago

Looking at Minitab's documentation for the Individuals Chart specifically, the calculations in the current visual correspond to the 'Nelson estimate' method

boyddt commented 3 months ago

Thank you for your comments and I'll look through the documentation. One last question, when using a P' chart in our environment, we set the limit sub-group limit to the max value of the denominator. This is done when our production numbers are greater than 1000. Not being a statistician, I don't know exactly why we do it but it is how we are instructed to configure Minitab. Can you app handle that feature?

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shauneccles commented 3 months ago

A simple, ugly workaround for this is to create a set of measures for SPC use which is just the base measure +0.

Need to be aware of the implications of this such (future dates in your date table will have 0 values so will need to filter dates at a visual/page/report level, and past dates before measurements began will also need filtering) but if you only have a small amount of measures it's doable.