Friday, October 16, 2009

The Stratford Theory of Numbers #7

As regular readers know, my theory holds that almost every number in a newspaper or magazine is wrong, because it has been misreported and/or misunderstood by the journalist. Here is a passage from the Listener editorial in the issue of 17 October:
In the past 20 years, the proportion of primary school children being driven to school has gone from 31% to 56%. The number biking is down by two-thirds, and the number walking has almost halved. Among secondary school children, the number of walkers is the same as 20 years ago, but biking is barely a quarter of its 1989 level, and the number being driven is up from 20% to 35%.
I don’t know whether these numbers are accurate. This being the Listener, no doubt they are. But I do know that they are incomprehensible. We are presented with percentages, fractions and raw numbers, and expected to draw a conclusion from comparing them all.

We can, most of us, convert the fractions to percentages or vice versa to make the comparisons – though we shouldn’t have to – but what we can’t do is tell what the last sentence means. In the last 20 years the number of secondary school children has grown and if the number walking to school hasn’t changed then the proportion has dropped – but by how much? Almost halved, as with primary children, or more than halved? Much more, or just a bit? Can’t tell.

And you couldn’t calculate it from the increase in the number of children attending secondary school – you need to know the number living within walking distance, which changes when circumstances change. In Auckland, my children walked to school. Here in the country, they have to go by car.

What would be meaningful would be a comparison over time between the number of children living within walking distance of school who do walk, cycle or are driven. But that would be asking a lot of a journalist, even a Listener one.

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