When looking at just one hospital, what does it mean if its survival is outside its predicted range?

Possible reasons for a hospital’s survival rate being outside its predicted range of survival:

1. Inaccurate data

Each hospital and the Office of National Statistics supply data on each child to the national audit body. Although the data submitted is of very high quality, there will always be some inaccuracies in such large datasets. If a hospital submits data where some of the data is very wrong or missing, then this will result in a wrong predicted range.

2. The formula doesn’t work well for that hospital

The statistical formula is applied to all operations at that hospital to calculate its overall predicted range of survival. Although the formula is as good as we can currently get it, it is not perfect. There will always be unique features about a child that affect their chance of survival that are not captured by national data collection and so cannot be part of a formula (e.g. the size of a hole in the heart). We will never be able to capture the whole medical picture of a child in a single formula. That means that the predicted range is the best possible guess for what the predicted range should be. If a hospital happens to have operated on a lot of children with unique features that affect their chances of survival but are not captured by the formula, the predicted range might be unfairly high for that hospital.

3. Chance

If the hospital’s data contains no errors and there’s no reason to think that the formula shouldn’t apply well to that hospital, then in 19 times out of 20, we’d expect to see a hospital’s overall survival range within the predicted range. This means that the hospital’s survival rate could be outside its predicted range just by chance (1 time in 20). (You can also watch our short video on how the predicted range is calculated.)

4. The chances of survival at that hospital are different to what are predicted by the formula.

The chances of survival for children at the hospital could genuinely be much higher or lower than what is predicted, which would make it more likely that the hospital’s survival rate would lie outside its predicted range. The national audit process is intended to check that no hospital in the UK and Ireland has chances of survival much lower than predicted. See What happens if a hospital’s survival is below its predicted range to find out what happens in such situations.