4 Replies Latest reply on Sep 14, 2018 12:16 PM by Cody Corbin

# Creating Control Charts based on the standard deviation of an average

Currently working on a workbook in which I am trying to create a control chart based on the standard deviation of the average job time. The LOD is basing itself on the particular job name and the number of jobs pertaining to that particular job name then getting the average of the total elapsed time in seconds. I would like to be able to use this average to generate the control chart as you could see from the second image. Using the average job time pertaining to each job set, return the standard deviation between the elapsed time and compare it against the bounds created. I would hope this is possible, as then this data will be illustrated on a box-and-whisker plot to show the distribution and whether or not the respective job runs out of the regular bounds or not.

I have been struggling with this solution for a few days so any kind of guidance would be super beneficial.

Thanks again,

Cody

• ###### 1. Re: Creating Control Charts based on the standard deviation of an average

Hi Cody

would need to see the workbook and how you constructed the viz

In words the first formula says " for each combination of Job name and Number of Jobs return the average total elapsed time "

That will create another layer in you data and that layers is NOT an aggregate in itself -

you can use the results of the LOD in other calculations - like STDEV or STDEVP - directly - don't know why you chose the table calculations version window_stdev?

What wat in the viz and what did the formula return ?

You need a range of values from the LOD to calculate an std dev and you will have to account for nulls in the lod level of data but you should be able to do it

Jim

If this posts assists in resolving the question, please mark it helpful or as the 'correct answer' if it resolves the question. This will help other users find the same answer/resolution.  Thank you.

• ###### 2. Re: Creating Control Charts based on the standard deviation of an average

Hello Jim,

I am working with sensitive information so I will not be able to share the workbook but however maybe I could get some assistance with the logic. I am essentially calculating the average per job name based on the number of jobs, that is the LOD avg job time. Then using the same start to the LOD i calculate the standard deviation and make those the control limits. Now the part that I am currently stuck on is that the average should give an average relative to the particular job not giving each a overall average, this would provide a line graph of some sort that would show when the average time is out of the threshold established.

I know it seems like a lot but everything is pertinent to the dashboard, need the average to compare it against the control limits, then like a compare function against the job subset.

Thank you for the assistance,

Cody

• ###### 3. Re: Creating Control Charts based on the standard deviation of an average

Cody see the link on how to provide dummy data   Anonymize your Tableau Package Data for Sharing

from the images you did provide you should be calculating the standard dev on the LOD expression and not on the eplapsed time

sorry but that is as far as i can go with some data and a workbook

Jim

If this posts assists in resolving the question, please mark it helpful or as the 'correct answer' if it resolves the question. This will help other users find the same answer/resolution.  Thank you.

• ###### 4. Re: Creating Control Charts based on the standard deviation of an average

Thank you for trying Jim, I ended up figuring it out.

- Cody