The gambler's fallacy 79
up an army of white-coated scientists with horn-rimmed spec-
tacles, and dedicated doctors with stethoscopes draped in
careless urgency. The invisible army will nod sagely in support of
each precise statement you make, and if the audience might
have doubted you they will be reassured by the phantom legions
who underwrite your figures.
Whatever the academic merits, single-stream schooling certainly pro-
duces more balanced children. Surveys have revealed 43 per cent fewer
psychological abnormalities among groups which...
(Just don't tell them that the abnormalities included self-esteem,
competitiveness and the desire to learn.)Remember to be exact, especially when you are being vague.We can be 90 per cent certain that Bloggs is the guilty man.
(And 100 per cent certain that you cannot prove it.)The gambler's fallacy
Few fallacies are more persistent in gambling circles than the
belief that the next toss (or spin, or draw) will somehow be
influenced by the last one. Gamblers, and others, are led into this
fallacy by confusing the odds against a whole sequence with the
odds against any event in that sequence.
The odds against a tossed coin coming down heads five times
in a row are easy to calculate. The answer is
1/2 x 1/2 x 1/2 x 1/2 x 1/2, or 1 in 32If the first four tosses, despite the odds, come down heads, the
chance of the fifth toss being heads is not 1 in 32, but 1 in 2, as it