Damned lies and statistics

A closer look at statistics in the news

Chris Cook

At the moment, the Department for Education is considering changes to the league tables and the exam system. This seems an opportune moment to make a simple point about qualification-awarding and accountability: English school examinations are subject to measurement error in a really big way.

Here is a simple thought experiment to flesh it out. Imagine a class of 100 students. Let us specify that each one has a “true” ability that means that one pupil should get one point, one pupil should get two, one should get three and so on – up to 100 marks. Now, let’s award this class one of 10 grades: 90+ gets you an A, 80+ a B and so on.

Let us assume that the tests are perfect. If that were the case, you would get ten individuals in each grade. Easy enough. But what happens if we start introducing errors into the test? We can do that with a set of exotically named (but very simple) “Monte Carlo” estimates, which I calculated using this simple spreadsheetRead more

Chris Cook

Last week, I went to Wolverhampton where I spoke at a local debate, organised by the university and Pat McFadden, the local MP, about the local authority’s school. I was the warm-up act for Lord Adonis, former schools minister, setting the scene about the city’s education system before his talk on lessons on school improvement.

It was interesting event – and the city is clearly considering its future and the role of education within it. There is – judging by my inbox – serious and deep interest in improving schools in the city. One of the things I sought to do was set out Wolvo’s position in relation to the rest of the country – and what statistics about the city tell us.

Here is my presentation: Read more

Kate Allen

If you’re going to have a bet this party conference season, take on an MP – that’s the obvious conclusion from an Ipsos Mori poll for the Royal Statistical Society, which suggests that our elected representatives are simply asking to be fleeced.

As part of its Parliamentary lobbying work, the RSS set a basic probability question for nearly 100 MPs. ‘If you spin a coin twice, what is the probability of getting two heads?’*

More than half of them got the answer wrong.

all MPs Read more

Emily Cadman

One of the more interesting aspects of Friday’s ONS release on the UK internet access patterns is the reasons why households don’t have internet access.

Much of the data release is as you would expect: more households have internet access, and more people are using computers daily, a trend especially noticeable among the young. Read more

Britain’s traditional measure of inflation, the retail price index, is broken and needs fixing. The error goes back decades, has cost taxpayers billions, is still costing the exchequer about £1bn a year and has resulted in the rise in living standards being underestimated. Few errors in statistical compilation are quite this serious.

 Read more

Chris Cook

One of my grand theories is that public policy types are generally bad at geography. Or, at the least, they underestimate the importance of where you live. Here, below the fold, are two zoomable maps, coloured by the school performance of local state-educated children. The map is based on where the children live, not where they go to school. To explain:

  • The colouring is red for weaker results and blue for better ones. Darker colours mean more extreme results. If you want detail on an area, click on any one of the blobs and it should give you a run down of local statistics, where possible.
  • Both maps are coloured according to FT score results: that is the sum of state-educated pupils’ scores in English, maths and their top three other subjects.    Other data, including official measures, are in the boxes that pop up.
  • On the first map, the geographical blobs are smaller than on previous maps: the lowest super output area in high density places, and the middle-layer output area in zones of low density (this way, we can show maximum detail).
  • That map can be quite frazzling. The second might be more to some people’s tastes. This is exactly the same sort data, just arranged by parliamentary constituency. Since they are bigger lumps, we can include more detailed data.
  • For the constituencies, I have given a barrage of results for all local children in state schools. But also the same just for FSM-eligible children, and for children dubbed “middle attainers” – kids who score in the middle tenth of results aged 11.
  • (NB – Where statistics are missing, it is prevent people combining data sources to work out something about individual children.)

If you want a tour, I’d recommend scrolling along the coasts. Check out some of the coastal towns, and look at the belt of towns and cities between Hull and Liverpool. Also, take a peek at how few dark red areas there are in London. In-borough variation is interesting, too: look at the massive variation within, say, Kent. Read more