Should we eat more fish or more ice-cream to boost PISA scores?

John Jerrim.

If anyone has ever read one of the international PISA reports or seen Andreas Schleicher present they will know that the OECD is rather fond of cross-national scatterplots. These illustrate the relationship between two variables measured at the country level.

Take, for instance, the chart below. This has been taken from one of Mr Schleicher’s blogposts, and illustrates the relationship between a country’s test scores and its rate of economic growth. It has been interpreted by the OECD as showing “that the quality of schooling in a country is a powerful predictor of the wealth that countries will produce in the long run”.

Source: Research by Hanushek and Woessmann, via the OECD Education and Skills Today blog

Sounds convincing, right?

The trouble is, correlation does not equal causation. And, despite the OECD’s obsession with such cross-country relationships, they can often deceive.

Should we eat more fish?

Of course, it is not only the OECD that produces such analyses. Academics do as well.

One of the more unusual examples I have found is this study by a group of epidemiologists. They look (I kid you not) at the relationship between average fish consumption and average PISA test scores.

Somehow, the study manages to find a strong positive correlation of around 0.6! It then goes on to conclude that a “linear association between fish consumption and PISA scores is likely” and that “it is plausible to assume that a higher level of fish consumption drives improvement at school level”.

As a nation of fish-and-chip lovers, this should be good news for our PISA scores…

But isn’t eating ice-cream just as important?

Getting kids to eat more fish is difficult. My little boy hates the stuff! He does, however, like ice-cream – and lots of it (who doesn’t?). If only eating ice-cream were as good for PISA scores as eating fish.

Well, apparently it is.

The chart below provides one of my all-time favourite PISA graphs. It plots the level of ice-cream consumption of a country against average PISA reading scores. There is actually quite a strong positive relationship, with around half the variation in PISA scores explained.

It also seems that the relationship is exponential (i.e. the line of best fit is curved upwards). Not only should we eat more ice-cream, but we should be eating lots of it.

The take-away message (no pun intended)

Hopefully, the point of this blogpost has become clear.

When the PISA results get released at the start of December, the international report and presentations given by the OECD are bound to include this kind of graph, along with stories about how ‘high-performing countries’ all do X, Y or Z.

Clearly, we should be treating any such interpretation of the PISA results with caution. There are likely to be hundreds, if not thousands, of reasons why some countries do well on PISA and others don’t. In reality, it is almost impossible to separate these competing reasons out.

What we do know is that overly simplistic “explanations” for the PISA results must be avoided. Organisations like the OECD have their own agenda, and it is just too easy for such groups to use the results to promote their own hobby-horses.

Other posts in this series can be found hereherehereherehereherehere and here.

Photos: fish by tkcrash123, ice cream by J Lippold via Creative Commons

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Posted in accountability and inspection, International comparisons

Paying for a private sixth form education: how much difference does it make?

Francis Green and Morag Henderson.

Britain’s private schools have again entered the public eye, with increasing concern over social mobility and social justice. There have been pressures for reform from several quarters. The most extreme was a September call for their ‘abolition’ from the annual conference of Labour, Britain’s main opposition party.

But whether one’s preference is for abolition, radical reform or no reform at all, confusion continues over what private schools actually do.

The question is: does private schooling in Britain actually improve children’s academic performance, beyond what would happen if they attended state schools, once account is taken of the characteristics of the children who attend them?

Read more ›
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Posted in Education policy, Schools

Is PISA ‘fundamentally flawed’ because of the scaling methodology used?

John Jerrim.

Every time PISA results are released, concerns are raised about the methodology that underpins the work.

One area that has come in for repeated criticism is how the test scores of students are actually produced, as in this article, which asked whether PISA was “fundamentally flawed”.

Such concerns were exacerbated by a seminal paper by Svend Kreiner and Karl Bang Christensen who claimed that their results indicated that using PISA to compare countries was “meaningless”.

Read more ›
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Posted in Evidence-based policy, International comparisons, Research matters

How much does private schooling raise your pay, and does it make you give more to the community?

Francis Green

Private schools find themselves in the news lately, more than they usually are. Boris Johnson became the fifth Old Etonian prime minister since the war, and immediately appointed a cabinet in which nearly two-thirds were privately educated, re-affirming once again what the Sutton Trust and the government’s Social Mobility Commission have been revealing about the political influence of the privately educated. At the same time, for the first time in many decades the possibility of radical private school reform has entered the political agenda. 

Formal evidence on what private schools do can help people evaluate views about Britain’s private school system and whether there is a need for reform. There are two important findings from our latest research which looks at a cohort born in 1990 and Read more ›

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Posted in Schools, Social sciences and social policy
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