The method used to collect data can have a significant affect on what the results seem to show. A good illustration of this is in British crime statistics.

There are two rival sets of statistics representing crime in Britain: the British Crime Survey and the police’s own figures. Neither is without difficulties.

The British Crime Survey has some clear limitations. Because it is based on asking members of the public about crimes in which they have been the victim, it has blind-spots. Victims of murders, for example, cannot respond to surveys, and so do not show up in the figures. Crimes committed against institutions (e.g. businesses), rather than individuals, are also omitted. Victimless crimes, such as drug use are overlooked by the survey too. The method in which the data is collected thus distorts the statistics, restricting their value.

The police figures are, in many ways, just as unsatisfactory. They only reflect reported crime, meaning that only a fraction of the more minor crimes committed make it in. This also means that any change in people’s willingness to report crimes will be indistinguishable from a change in the number of crimes committed; how are we to tell whether crime is falling, or confidence in the police is falling? Add to this the fact that the way in which crimes are classified has changed over time, and it becomes clear that the numbers can be misleading.

For these reasons and more, crime statistics cannot be taken at face value. Interpreting the figures is a complicated matter.

The Tory party today attacked Labour for what it claimed is excessive spending on public relations: over £322 million / year. This includes the wages of over 3200 press officers. Things weren’t like this under the previous government, the Conservatives have pointed out.

As it was reported in a Guardian article, the Conservatives’ complaint was supported almost entirely by a comparison of current and past figures on spending. The article repeatedly contrasted the current figures with those from nine years ago, when the Tories were last in charge.

In 1997 the cost of government PR was just a third of the current £322 million at £111 million, it points out. Back then there were just 300 press officers in Whitehall, compared to around 1800 today, it continues. Tax-payers money is being wasted, it is inferred.

Now the government spending on PR does seem over-the-top. However, simply comparing current figures with previous figures doesn’t prove that.

Things have changed since 1997; the rise in 24-hour news and the increase in demand for news that it has created, for example, means that there is greater pressure on the government to provide information to the press than there was before. Other factors may also justify a rise in spending.

Besides, for all that is said in the article it may be that the Tories were guilty of under-spending on public relations. If all we have is a comparison of two sets of figures, then how are we to decide whether current spending is too high or past spending was too low?

Simply looking at the past and assuming that things should be the same now is a logical error: the appeal to history fallacy. A little more is needed to show that Labour have been over-spending on spin.

Today, Ryanair has threatened to sue the government over the security measures that have recently been imposed at airports. Since a plot to detonate bombs on planes traveling from the UK to the US was uncovered a few weeks ago, air passengers have faced tight restrictions on what hand-luggage they are allowed to carry, and stricter checks than were previously in place when boarding.

The measures have made air travel from the UK extremely difficult. Passengers have endured long delays, and many flights have had to be cancelled, negatively affecting airlines. A Ryanair spokesperson argued that the measures are unnecessary, and said that unless they were lifted Ryanair would be seeking compensation from the government for imposing them.

To support this claim that the security measures are unnecessary, the spokesman made a comparison with the 7/7 Tube bombings. After the bombings, he pointed out, the government got the Tube service back to normal within a matter of days. There is therefore no reason, he inferred, for the current security measures at airports to continue weeks after the plot to bomb aircraft was uncovered; things should be back to normal by now.

This argument overlooks important differences between the two cases; it draws a weak analogy. For example, the Tube bombings did not involve the discovery of any new threat, and so once the damage done had been repaired and the crime scene examined, things could return to normal. The discovery of the recent terrorist plot, however, raised a new danger: the possible use of liquid explosives. It therefore required new security measures to be introduced indefinitely.

This difference between the cases that the Ryanair spokesman compared means that the comparison can’t support the conclusion that he drew from it.