Grammar schools

A very quick post here, about grammar schools and Graham Brady, the Conservative MP who is no longer in David Cameron’s team. The use of statistics here is shocking.

Mr Brady sent some data to the Times, showing that grammar schools ‘give a lift to results of all around them’ which essentially hinges on the fact that GCSE results of the population in areas with grammar schools is better than those of the populations in the areas without them. Somehow this ended up as being translated to improving everybody’s exam results. A clear case of taking an average or mass description, and mistakenly deducing that this applies to all the individuals in the population. And of course, there could also be a correlation with other causes.

First, it’s easy to see how the total number of GCSE success stories (the 5 A-Cs) can increase overall but still be unfair. If half the schools are grammars and they manage to get an extra 2000 pupils to this level (who otherwise would not have done), while the other schools fail to get 1500 pupils to this level (who in a comprehensive system would have acheived it, but didn’t in a ‘secondary modern’) then the total success rate increases. So 1000 people are boosted by 500 people being pulled back (this is what some research tells us), and so we need to ask who this effects and how. It can still be unjust, because the raising of an average doesn’t necessarily mean all are raised.

Second, the simple measure (5A-C) doesn’t take into account other changes. Perhaps some who would get 4A-Cs in a comp. then get none in a secondary modern… none of the figures tell us anything  about this.

And lastly, there can be other causes (the classic spurious correlation), or more complicated causes. Perhaps the places where grammars survive still have these schools because the population of parents is better educated and thus more likely to have had a grammar education themselves. Or perhaps middle-class people use their money to move to grammar school areas, believing them to be better, and these people are more motivated to help their kids do well at school.

Without more and better evidence… we just don’t know.

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Filed under Politicians, Statistics and simplicity

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