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248 Biases in probability assessment
(3) In the USA, which cause of death is most likely out of each pair:
(a) a stroke or an accident;
(b) influenza or an aeroplane crash?
(4) Eight percent of people interviewed for jobs at a company have a
criminal record. Given below are the notes made by the interviewer
on one applicant, Jim X. These notes have been randomly selected
from the files of interviewed candidates.
Jim had an unshaven, scruffy appearance. Though his clothes looked
expensive they did not fit him well. He never made eye contact during
the interview and he had a strange, hard look about him. When I cracked
a joke he failed to laugh. His handshake was weak and I noticed a scar
on the back of his hand. He said he had no hobbies or family and his
general demeanor was unfriendly, and even a little contemptuous.
Estimate the probability, on a 0 to 100 scale, that Jim X has a
criminal record.
(5) A box contains 100 light bulbs of which half are defective. A quality
control inspector is about to select six bulbs randomly from the box.
Which of the following sequences is most likely to occur:
1st bulb 2nd bulb 3rd bulb 4th bulb 5th bulb 6th bulb
A defective OK defective OK defective OK
B defective defective defective OK OK OK
C OK OK defective OK defective defective
(6) A man has been driving for 40 years without having a road accident.
A friends tells him that the chances of him being involved in an
accident in the next five years must be high because the probability
of an individual driving for 45 years without an accident is low. Is
this thinking correct?
(7) In the British National Lottery people choose six numbers (from
1 to 49) which they hope will be randomly selected in the draw.
When the lottery started, a newspaper advised: ‘... sometimes
week after week, a certain number may resolutely refuse to put in
an appearance. It becomes ‘‘overdue’’, and you could reason that
therefore it is bound to turn up soon – the so-called cold number
system.’
Would choosing ‘cold numbers’ increase your chances of winning
the lottery?
(8) During the summer, a brewery’s sales of canned beer are largely
influenced by chance factors, such as the weather and the number