"The risk of terrorism increased after 9/11"

There's no evidence to suggest the risk of terrorism increased after 9/11. In fact, US State Department figures published in 2004 show terrorism at its lowest level in 35 years. (See graph below, and http://www.state.gov/s/ct/rls/pgtrpt/2003/31751.htm)

Some media coverage gives the impression that 9/11, as an event, somehow led to or caused an increased threat of terrorism. This is an example of a logical fallacy known as Misleading Vividness, in which the occurrence of a dramatic event is taken to mean that such events are more likely to occur (despite statistical evidence to the contrary).

Scaremongering Fallacy

The "increased terror threat" fallacy is used by government to justify new freedom-eroding legislation – and also to justify the spending of billions of pounds of public money on an ID card scheme of questionable benefit in combatting terrorism (a former head of MI5 cast doubt on the usefulness of ID cards in this respect).

According to the MIPT terrorism knowledge base, the total number of US and UK (including Northern Ireland) fatalities caused by terrorism in the five years after 9/11 was 74, compared to 68 in the five years before. The corresponding totals for Iraq are 15,763 and 12, respectively. That should put fear of terrorism into perspective for UK and US citizens.

Unfortunately, as Michael Bond reports in New Scientist (19/8/06), people base their fears more on the vividness of events than on the probability of them reoccurring. And since television presents very vivid coverage of any attack (or foiled attack, rumoured attack, etc) on UK or US soil, it is "destroying our probabilistic mapping of the world", according to Nicholas Taleb, professor in the sciences of uncertainty at the University of Massachusetts (quoted in New Scientist, 19/8/06).

The "increased terror threat" fallacy was also used in government PR in the run-up to the 2003 invasion of Iraq (eg Saddam's WMD + increased terrorism risk = urgent need to invade Iraq). Ironically, the invasion of Iraq has led to a huge increase of terrorist attacks within Iraq.

Source: http://www.state.gov/s/ct/rls/pgtrpt/2003/31751.htm