Spin and Statistics

http://www.thisisjersey.com/2008/09/27/75-increase-in-burglaries/

"75% increase in burglaries" screams the headlines.

POLICE are urging Islanders to lock doors and windows after the number of house burglaries soared by 75% this summer. A total of 150 homes have been burgled since May compared to just 86 during the same period last year.

This is a perfect example of what Darrell Huff called "How to Lie with Statistics". Of course, any burglary is bad, and I'd hate to be burgled, but let's look at the real figures.

Assume - and there are more than that - a mere 20,000 households in Jersey - flats, betsits, houses.

86 / 20,000 = 0.43 %
150 / 20,000 = 0.75%

Now recast the text as:

Burglaries sour up from 0.43% of dwellings to 0.75% of dwellings!

Not quite as impressive, but in fact more representative of the true picture. When you have small numbers, 86, 150, a jump can seem like a lot if expressed as a percentage.

Wicca, is at the moment, for example, often described as "the fastest growing religion" simply because it is expressed in percentage terms like this, taking one figure as a percentage increase on the other.  It sounds good, but all it really means is that it actually has a quite small membership, so that any increase features heavily. If expressed per head of the population, the figures rapidly reduce in significance.

It is a pity the JEP didn't ask the statisticians doing the survey (more on that later) for advice before working out the figures and coming out with a headline that is needlessly alarming.