Why does the width of the predicted range differ between hospitals?
A predicted range of survival is calculated individually for each hospital, taking into account the children it treated. If the chances of survival at that hospital are as predicted, then we expect the hospital’s survival rate to lie within the predicted range 19 times out of 20. The width of the predicted range varies with the number of operations a hospital has done, because of unforeseeable factors that occur. We know that sometimes unforeseeable factors will affect a child’s survival – though, of course, we cannot predict exactly what they will be and when they will occur. In a smaller hospital that performs 100 operations per year, even if one more or one fewer child survives due to unforeseeable factors, this could make a big difference to that hospital’s overall survival rate. However such unforeseeable factors would have less influence on the overall survival rate of a larger hospital performing 1000 operations. This is why hospitals doing more operations have a narrower predicted range than hospitals doing fewer operations.
- Unforeseeable factors
It is impossible to predict precisely what is going to happen in an individual operation. This is partly due to the inevitable inability to predict the future with certainty – all people are physically unique and will react slightly differently to medicines, anaesthetic, surgery and no heart problem is exactly the same as another.
There are also factors that we suspect may influence the outcome but cannot be included in the statistical formula because no routine audit data on them is collected, for instance the size of a hole in the heart.
Together, we call these all “unforeseeable factors”.
- Survival rate
- The percentage of operations where the child survived at least 30 days after their operation.
- Predicted and Extended Predicted range:
We expect a hospital's overall survival rate to lie within its predicted range 19 times out of 20.
We expect a hospital's overall survival rate to lie within its extended predicted range 998 times out of 1000.
An illustration of how we present a hospital's survival rate (black dot) in the context of its predicted range (dark blue bar) and extended prediction range (light blue bar) is given below:
