Readmissions rate fallacy

Today’s piece in Kaiser Health News that hospitals’ readmissions rates are flat appears to suggest various ongoing efforts to cut readmissions are failing and failing badly.

According to the Medicare data used by Kaiser, the readmission rate for heart failure was 24.8% in 2008-10 and 24.7% in 2009-11 giving us the 0.1% decline cited by Kaiser. Comparing 2011 to 2008, this is a 0.3% difference, still not sufficient to convince us that there is a real change.

But don’t write off those efforts yet as there may be a silver lining in the numbers. In fact some simple math suggests that a more meaningful measure of readmissions has fallen as much as 3%.

Readmissions are calculated as a proportion of discharges. What if there are fewer admissions and therefore fewer discharges – in other words, if people who are less sick are being treated in out-patient settings more often rather than being admitted? If that is true then the denominator for the readmissions calculation (the # of discharges) will have dropped without a commensurate drop in the numerator (the # of readmissions).

So we thought it would be interesting to see what happens if we look at the change in admissions and factor that into the calculation.

It turns out the admission rate for heart failure did indeed drop from 2.01% in 2008 to 1.84% in 2011 at a fairly consistent rate of about 3% a year. Had this admissions rate remained flat rather than dropping like this, we would have seen the readmission rate drop by an additional 3% per year. Now that’s pretty good!

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