Control chart applicable?

My response from Elsmar:

TAT = Turn Around Time? Is this a set time on the clock (for example the radiologist must submit their report by 9 AM) or is it teh allowed time to complete the report from the time of submission (for example, the readiologist has 2 hours from the submission to submit their report).

Yes an I, MR chart will work for TAT compliance. The subgroup for what I have described above is typically a day, but weeks and months will also work.

If TAT is what I described above, more insightful chart is to plot the actual time it took the radiologist to complete the analysis for each individual submission. You can still use an I, MR chart.

As a point of clarification, sampling error is only a convenient way of ‘describing’ the variation from subgroup to subgroup from an infinite real process stream. (It derives from actual sampling error when taking small samples from a finite population). In real life we have actual process variation as well as ‘sampling error’ when taking small samples from an infinite stream of work. Control charts still work for these infinite streams because the variation of the process is ‘random’ and homogenous.

 

You might find the following article useful:

“What About p-charts?”, by Donald Wheeler, published by Quality Digest.

he describes why the I MR chart is so useful and the limitations of the p chart even for proportional data. certain assumptions do need to be met to use the p chart and the I MR chart has fewer assumptions.