by Steve Bain

Created on: February 17, 2009

Statistics are everywhere. Every newspaper and every news bulletin is full of them. They form the backbone of countless amounts of articles. It seems that for a piece of analysis to have any credibility whatsoever, it needs statistics. But how much should you take from them? Depending on how you compare two things, there are several different percentages you could find. The range of percentages, all of which are perfectly valid, leaves a writer in a position to manipulate a story by choosing the number which best fits in with what he wants to show.

The best way to illustrate this is with an example. Imagine ten cars past my house in one hour. The next hour, only 9 cars pass. There are four different percentages I can choose to represent this. These are:

10% There has been a 10% drop in cars passing my house

90% The amount of cars passing my house is 90% of what it used to be

111% The amount of cars passing in the first hour was 111% of the amount in the second hour

11% The first hour had 11% more than the second hour

All of these percentages are perfectly valid. I won't bore you with the maths behind them but they're all quite simple to work out. The only difference between them is the words that describe each percentage. Although all four statements look quite similar, each one is fundamentally different.

The first describes the change from hour one to hour two.

The second describes hour two in terms of percentage of hour one.

The third describes hour one in terms of percentage of hour two.

The last describes the difference from hour two to hour one.

Confusing, I know, but each of the four percentages describes the change from a different perspective. They all, however, describe the same event. More importantly, they can leave the reader with different impressions. Average Joe won't pay much attention to the words around the figure, just the figure itself. A 10% drop seems like a quite a significant drop, while 111% seems like a massive rise. It would seem then, that the number itself is meaningless.

So what can you learn from this? Well hopefully you'll stop judging an event by the percentage labelled onto it, and realise that the words surrounding the number are much more important. The number is meaningless if not accompanied by a statement that accurately tells us what the number describes. And let's not forget, it is entirely possible that I just wasn't looking when a car drove past in that second hour.....

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