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Control chart builder: why is LCL =Avg = UCL when a time axis is added?

Monomorphist

When building a run chart in control chart builder and I drag the parameter onto the y-axis, I get correct spec limits and standard deviation. As soon as I drag the time column on the x-axis (subgroup), LCL equals Avg equals UCL. Why? Is there a way to have the time/date on the x-axis and still get a result?

I've attached a screen record to demonstrate the issue. Note, too, that the h:min:s turn to 00:00:00 on the x-axis

By the way, if I go through Legacy Control Charts -> IR, it works, LCL<Avg<UCL and correct h:min:s on the x-axis

Kofi

JMP_ControlChartBuilder1.mp4

Accepted answers

Mark_Bailey

I suggest that you examine the Time data column. There are several ways to determine if there are multiple rows with the same time.

Select Tables > Summary and put Time in the Group role.
Change the modeling type to Nominal and launch Distribution with Time in the Y role.
Change the modeling type to Nominal and launch Distribution with Time in the Y role.
Change the modeling type to Nominal and launch Tabulate with Time in a grouping role.

What did you find?

And what version of JMP are you using?

All comments

Mark_Bailey

There is something wrong with the the values in the Time data column. JMP detects multiple observations for the same value and so it switches from a XmR pair of charts to a XbarR pair of charts. Change the chart type back to Individual and Moving Range.

Monomorphist

I rather suspect there's something wrong with the Control Chart Builder.

When I try to create a IR chart through the Control Chart Builder, JMP tells me that at least 1 sample has sample size > 1, hence can't create IR, has to make XBar (and consequently doesn't allow me to change back to individual and moving range)

When I try to create a XBar chart through the Legacy Control Chart menu, JMP tells me that no sample has sample size > 1, hence it can't create XBar, has to make IR.

What now? Does any of my sample has sample size >1 or not? Control Chart Builder platform says yes, Legacy Control chart platform says no. That's a bug!

Simple as that.

My guess: Control Chart Builder can't read it's own date-time format. Sets all h:min:s behind the date to 00:00:00 and then, yes, plenty of observations at the same time (=day/date). JMP needs to fix this

Mark_Bailey

I suggest that you examine the Time data column. There are several ways to determine if there are multiple rows with the same time.

Select Tables > Summary and put Time in the Group role.
Change the modeling type to Nominal and launch Distribution with Time in the Y role.
Change the modeling type to Nominal and launch Distribution with Time in the Y role.
Change the modeling type to Nominal and launch Tabulate with Time in a grouping role.

What did you find?

And what version of JMP are you using?

Monomorphist

Hi Mark,

that's a good one. Turned out the data table had 1 day entered twice = double entries.

Still remains the question why one platform picks up the duplicates and the other doesn't...?

I'm using v15.1.0