Because if you don’t you might end up like Tim Blair:
Big call from Tim Lambert: “Crime and violent crime in Britain peaked in the early 90s and [have] since plummeted.” His source? The British Crime Survey, an annual affair which asks some 40,000 Brits if they’ve been encrimed during the previous year. Is it trustworthy? Depends which side you’re on:
The political discussion about crime is often a numbingly boring argument about statistics. Overall crime recorded by the police seems to have risen (so the Conservatives rely on this statistic) while crime reported by the public seems to have fallen (so Labour rely on that).
I’d lean towards the official police figures myself (although jerked-around crime counting methods make comparisons problematic), mainly because they’re, you know, official police figures. The British Crime Survey is just a survey.
Blair might as well have said “Does 2+2=4 or does 2+2=5? Depends which side you’re on.” It doesn’t depend on which side you are on. There is a right answer and a wrong answer. Not all crime is recorded by the police. The police recorded 5.9 million crimes, while the BCS, which included crimes that weren’t recorded by the police, estimated 10.9 million crimes. Obviously the BCS number is closer to the right answer.
I suspect the reason why Blair is so dismissive of the BCS is that he doesn’t understand enough statistics to tell the difference between a good survey and one that is worthless. An example of a worthless survey was published by the Bulletin to accompany Frum’s article advocating the death penalty.
While Australians are evenly divided on whether the death penalty should be reintroduced here, according to an exclusive Bulletin poll, more than half (56%) of respondents believe that the government should not try to persuade the Indonesian government to reduce the sentences of the Bali Nine — which include the death penalty for ringleaders Andrew Chan and Myuran Sukumaran.
However, if you look at the full poll results, you will discover something much more interesting: 66% of Australians are male! How come? Well the Bulletin reports that the poll was conducted by CoreData. If you check out their page, you find that they pay people to do surveys over the Internet. For a survey to be representative of the views of Australians, you must have a proper random sample, where each person is equally likely to be surveyed. The CoreData sample was biased in two different ways: first it only included people with Internet access, and second, even amongst Internet users, it just sample people interested enough in doing surveys to sign up with CoreData. As a result, the survey was worthless — the results do not reflect what Australians think. Nor are 66% of Australians male.
But if a survey uses a properly random sample, where each person is equally likely to be surveyed and has a large enough sample size, the results are reliable. The BCS has both of these properties.
If you study statistics, you can learn the difference between good surveys (like the BCS) and worthless ones (like the Bulletin’s). And if you don’t know enough statistics to tell the difference, you can always find someone who does and ask them. Something Blair and the Bulletin might consider next time.