So how big or- how bad- is the gradient? Some comparative evidence may be useful. Making comparisons across countries is somewhat perilous. But I think one can say something with the large datasets available now. Using PISA I regress the reading score against an index of SES (the ISEI index due to Harry Ganzeboom if you are interested). No other controls are included since they might mop up the effect.
So the regression coefficent gives a scalar measure of the extent to which high SES is associated with high reading scores. One might call it marginal inequality as distinct from conventional measures of inequality which look at variation round the mean.
Two questions of interest are:
- Where does Ireland stand?
- What sort of countries have a high SES gradient?
The results are in the graph below.
In terms of marginal inequality, Ireland is about average. Our SES gradient is below the Anglo-Saxon countries (USA, GB) and also France but higher than the Nordics (Finland, Sweden) & Southern Europeans (Greece, Spain).
Aside from Finland there is pronounced upwards relationship: countries with a high SES gradient (which is presumably a bad thing) also have a high average score (a good thing). Is it a price worth paying, one might ask?