Expected mortality explained

Documentation update

I updated the EACTS Congenital Database documentation by adding description of the Quality of Care and the Expected mortality.

The open secret revealed

What I didn't write in the documentation is that the expected mortality works well as a replacement for the Aristotle Score. It has significant advantages over ABS. If you're the EACTS Congenital Database member, you can see it for yourself. Go to the Quality of Care charts here and:

  1. Change “Hospital Survival Axis“ to “30-day Mortality Axis“
  2. Change “Basic Score Axis“ to “Expected Mortality”
  3. Change “Split by surgeons” to “No unit split”
  4. Change “No procedure split” to “Procedures”
  5. Click the “Generate Report” button

You should see that for every procedure, the expected mortality matches the actual mortality. This is exactly how the expected mortality works. If the bubbles aren't perfectly in line, it's only because the mortalities per procedure were estimated some time ago and the data changes since then.

Let's check the same with the Basic Score. If the Basic Score matches the actual mortalities, the bubbles should be placed along the line, just like with the expected mortality. Go to the report form again (you can use the “Back” button in your browser).

  1. Change “Hospital Survival Axis“ to “30-day Mortality Axis“
  2. Leave the “Basic Score Axis“ option
  3. Change “Split by surgeons” to “No unit split”
  4. Change “No procedure split” to “Procedures”
  5. Click the “Generate Report” button

What you actually see, is nothing like a line. It's just a cloud, with bubbles spread randomly around. There are procedures with high ABS and low mortality. The opposite cases are also present. There isn't any visible relation (not mentioning the accuracy).

Careful with statistics

There was an attempt to verify in 2005 the correlation between the ABS and the mortality. The statistical study showed that the ABS factor is significant for the mortality model. Statistically, patients with high ABS had higher mortality than patients with low ABS.

Let's take a closer look at the data. Procedures are not equally popular. Some procedures are being performed more often than others. In fact, there are just few procedures which concentrate the majority of the population. In statistical study, it was enough to have just two procedures, one with low mortality and low ABS and second with high mortality and high ABS. The rest of procedures could have random values of the ABS and the statistical calculation would still show ABS as a significant factor of the mortality model.

It shows how careful one should be with statistics. Before the statistics are applied, the bare eye should be used.

Conclusion

Don't use the Aristotle Basic Score for the Quality of care evaluation. Use the expected mortality, it's accurate and simple to understand.

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Author: automatthias

You won't believe what a skeptic I am.