WS MoreOrLess: Testing the PISA test
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What is PISA and why is the latest international education league table creating waves?
This is the short edition of More or Less, first broadcast on the BBC World Service.
Hello and welcome to More or Less on the BBC World Service. I'm Ruth Alexander. This week, an International Education League table creates waves.
The UK is falling behind global rivals in international tests taken by 15-year-olds. US test scores remain stagnant, while other countries see rapid rise.
15-year-old school pupils in 65 countries sit tests, and every three years the results are compared. This time, maths was the main focus. But there are some who say that the people who design the test must try harder. We'll be exploring these concerns. But before we go any further, if you're anything like the More or Less team, you'll want to prove to yourself that you can answer a maths question aimed at a 15-year-old. So, introducing Quizmaster Charlotte MacDonald.
The PISA questions are divided into six levels of difficulty. So I thought, if you're listening to more or less, you're not daft. So we'll plunge straight in at level two. Helen's got a new bike. It has a speedometer which tells her the distance she travels and her average speed for the journey. Helen rode four kilometres in the first ten minutes and then two kilometres in the next five minutes. Which one of the following statements is correct? Is it A. She rode faster on average in the first part of the ride than in the second. B. She rode at the same speed the whole time on average. C. She rode more slowly in the first part of her journey than in the second part. D. You can't tell.
Well, she rode four kilometres in ten minutes and then half that distance in half the time, two kilometres in five minutes. So the answer is B. She rode at the same speed the whole time on average.
Correct. Now, 96% of 15-year-olds in Shanghai, Hong Kong and Singapore managed this level of question in the test. The average was 77%.
How does the PISA test sample 15-year-olds and what do the headline results show?
Now, the five top performers in this big international test are all in Asia. Shanghai is at the top of the class, followed by Singapore, Hong Kong, Taiwan and South Korea. Countries like the US and the UK are middling, and Peru languishes at the bottom of the league, with the likes of Indonesia, Brazil and Tunisia not far behind. Tunisia, by the way, is the only African country that at the moment takes part in these voluntary tests. The results from PISA, the Programme for International Assessment run by the OECD, are taken as gospel by the media and many policymakers. But should they be?
I think that the whole PISA enterprise could do with a lot more external review in terms of its statistical methods, which are unbelievably complex and rather opaque.
Professor David Spiegelhalter from the University of Cambridge's Statistical Laboratory. But before we go on... Question number two.
This is a level three question, so it's a little harder. Chris finds two cars at a local car dealer. They each have different size engines. Which has the smallest? The one which has a 1.79 litre capacity or the one which has a 1.783 litre capacity?
Well, this one's quite easy. The answer is 1.783. If we rounded it to two decimal places, it would round down to 1.78. Correct.
Now, Shanghai were the top scorers at this level. 89% of 15-year-olds got this level of question right. Now, that OECD average was 55%.
Thanks, Charlotte. Around 4,000 children in each country take part in the test, half a million in all. They get about two minutes per question. The test is made up of about 400 questions, and each child is given about 50 of them to answer. It means that the children answer different selections of questions. PISA designs the test like this to make sure a breadth of subject areas and skills are covered. It makes sense, but it also creates a problem. PISA has to use a statistical model to extrapolate from each child's answers how they would have answered the other 350 questions had they been given them. David Spiegelhalter says this practice raises its own questions.
These plausible values, I think, are open to some criticism because they're predicted conditional on, in fact, knowing the difficulty of the questions as if these are fixed constants, even though they're only estimated based on a subsample of students, and assuming that the difficulty is the same for all students around the whole world.
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