Comparing Value-Added between Qualification Types

Understanding the National Value-Added and IGCSE Value-Added: Why they’re not directly comparable

Many schools that use a mix of standard GCSEs and International GCSEs will use value-added measures to review departmental performance. In doing so, it can seem entirely reasonable to compare your standard GCSE results against the National value-added and to compare your International GCSE results against the IGCSE value-added. However, it’s important to understand that although the National value-added and IGCSE value-added both use national scores as their baseline, they are based on very different samples and cannot be fairly compared.

This article explains:

• How the National value-added and IGCSE value-added are calculated
• Why the two measures differ
• How to interpret them correctly to avoid misleading conclusions

How Value-Added Is Calculated

We offer three different types of predictions and value-added:

• National GCSE Value-Added
  Based on results from a broad range of schools, primarily state schools across the country, and uses national scores as a baseline. This provides a nationally-representative benchmark for schools.
• Independent schools Value-Added
  Based on results from students in independent schools only and uses independent schools’ scores as a baseline.  This provides an independent schools’ benchmark for independent schools.
• IGCSE Value-Added
  Based on International GCSE results only from students in independent schools and uses national scores as a baseline. The students taking International GCSEs tend to have slightly higher abilities than the other students in independent schools taking standard GCSEs. Although national scores are being used as the baseline this is a very different benchmark to the National value-added but instead is much closer to the independent schools value-added.

How the 3 types of value-added typically compare

The chart below shows the 3 types of predictions by students’ national scores for GCSE (9-1) English Literature. (Here the independent schools’ predictions have been adapted to use national scores). Different GCSE subjects will have different regression lines and different results, but English Literature is fairly typical of the differences we see. Independent school students have average national scores around 112. At that score the difference between the national and independent predictions is 0.9 or so, just below a grade. The IGCSE regression lines tend to be close to the independent school regression lines but a little bit higher still - the difference here between the IGCSE prediction and the National prediction is 1.1 grades. In this example, that difference of 1.1 grades will be roughly equivalent to a difference of 1.4 of a standardised residual between the two types of value-added.

So, the National value-added and IGCSE value-added are not comparable, and there can be significant differences between them, because the underlying comparison groups differ:

• The National GCSE value-added represents the progress made by students nationally, the majority of whom will be in state schools.
• The IGCSE value-added represents the progress made by students in the high-attainment independent schools that opt to use International GCSEs.

Best Practice for Schools

It can be useful to look at results from the different types of value-added, but it is important to only compare departments within the same value-added type and not to mix and match.