“…What we can call a 'transfer principle' also applies to the Index -that is to say, if equity is transferred from one pupil or group of pupils with a lot of it, to another pupil or group of pupils with a shortage of it, the resulting distribution becomes more equal -which is not the case with other school effectiveness metrics like CVA. It is easily interpreted, can track changes over time, can act as a prompt for improvement and can give fairly immediate feedback to policy-makers (Sammons et al 1997;Van Damme et al 2002;Thomas, Peng, and Gray 2007). This is not to suggest that the Index does not have its disadvantages: it measures equity, but on its own does not measure opportunity, capability or wider aspects of social injustice; like other school effectiveness measures, indices for different subpopulations cannot be averaged to obtain an index for the whole population; and as with all school effectiveness measures, if desirable commodities (like how schools encourage a range of intellectual, sporting and cultural interests among young people, enable friendships and develop the ability to interact socially) are not counted in the input, they cannot be reflected in the output.…”