Confidence in results
Attainment and progress measures are based on a given set of pupils' results for a particular test paper on a particular day.
The same pupils may have achieved different results on the day or the school would almost certainly have shown slightly different results with a different set of pupils, even with the same levels of prior attainment. Yet the school could be equally effective.
This causes us a degree of uncertainty that we should take account of.
The uncertainty of a value added score as a measure of school effectiveness can be presented as a confidence interval. This is a range of scores within which you can be statistically confident that the 'true' school effectiveness will lie; so a school's true result will be somewhere on the line but you will not know where.
Describes how smaller schools have larger confidence intervals. These confidence intervals are often displayed using vertical bars with a central black rectangle.
Graphic showing various confidence intervals for large and small schools above and below national median. The longer the vertical bar, the smaller the confidence level.
Some graphs show the range of typical results in addition to confidence intervals. The examples shown here are from the learning achievement tracker.