Numbers game

December 17, 2005

Hurricanes as usual
Statistics from the US National Hurricane Centre suggest that, contrary to appearances, major hurricanes are not becoming more frequent. On the standard Saffir-Simpson scale, a hurricane is classed as "major" if it reaches at least category three. From 1851 to 1900, there were 27 such storms in the US. Between 1901 and 1950 there were 34. But between 1951 and 2000, the number fell to 28. The peak decades of activity in the 20th century were 1931-60, with no fewer than 26 of the century's total of 62 major hurricanes. And in the three decades from 1971 to 2000, there were only 14, an average of only 4.67 per decade compared to the 1851-2004 average of six. Between 2001 and 2004 there were three major US hurricanes, a per-decade rate of between seven and eight, slightly higher than the long-term average. This is a rise on the rates of the three decades previously, so not surprisingly people perceive an increase. But as we have seen, 1971-2000 was a period of very low activity, so a rise was only to be expected.

Prison works
Outrage is expressed by liberal commentators at the news that the prisons of England and Wales are packed full with nearly 80,000 prisoners. How can this be, they ask, when crime is falling? Since 1995, for example, burglary has fallen by 60 per cent and violent crime by 46 per cent. In contrast, the prison population has virtually doubled in that time.
There are a number of explanations for the drop in crime. Increased home security, for example, has helped reduce burglary. But what is often not understood is that it is precisely because the prison population has increased that crime has fallen. The prison population was constant in the 1980s, then began to rise under Michael Howard, a policy which Labour continued. The increase reflects an increased readiness by judges and magistrates to pass custodial sentences. And it has deterred crime. The same phenomenon has been seen in the US, where the crime rate per 100,000 population is about half that of Britain. From their peak around 1990, violent and property crime rates have fallen by one third. And the prison population has doubled over this time.

Unfair on sharks
Every time a shark, particularly a great white, attacks a human, it causes great alarm. Australia is one place notorious for such attacks. But since 1791, only 630 instances of shark attacks on people have been recorded, about three a year, and only about 30 per cent proved fatal. Worldwide, the number of deaths caused by sharks each year rarely reaches five. On the other hand, it is estimated that up to 1m sharks a year are killed by humans. Perhaps the fish should beware of "people-infested" waters?