Probability judgement

AO1 Probability judgement ‘Probability’ refers to the likelihood of an event occurring, such as the likelihood that a horse will win a race or that a coin will come down heads. Some people are better at judging the probability of events than others, in particular, believers may underestimate the probability that certain events may simply happen by chance and therefore reject coincidence as an explanation for paranormal events. Thus Blackmore and Troscianko (1985) suggest that paranormal experiences are a kind of cognitive illusion resulting from a failure to accurately judge probability. The result is that certain people underestimate probability and attribute causality when in fact the events are simply random.

AO1 Probability judgement Repetition avoidance – One of the methods used to test probability judgement (or misjudgement) is repetition avoidance in generating random numbers. Participants are asked to produce a string of random numbers and the number of repetitions is counted. In a true series of random numbers there are repetitions but people who underestimate probability are less likely to produce such repetitions. Brugger et al. (1990) found that people who believe in paranormal phenomena (‘sheep’) avoid producing repetitions more than nonbelievers (‘goats’), illustrating the link between paranormal belief and probability misjudgement.

AO1 Probability judgement Questions about probability – Blackmore and Troscianko (1985) asked participants various questions including the birthday party paradox – how many people would you need at a party to have a 50:50 chance that two of them will have the same birthday (not counting year)? Possible answers were 22, 43 and 98. More goats than sheep got this right (the answer is 23).

AO1 Probability judgement Questions about probability – Blackmore and Troscianko (1985) asked participants various questions including the birthday party paradox – how many people would you need at a party to have a 50:50 chance that two of them will have the same birthday (not counting year)? Possible answers were 22, 43 and 98. More goats than sheep got this right (the answer is 23).

AO2 Probability judgement Contrasting research evidence – Not all research has found a difference between believers and nonbelievers in terms of their probability judgements. Blackmore (1997) concluded that both believers and nonbelievers are equally accurate in judgements of probability. One reason for the different findings from various studies may lie in the way that ‘belief’ is measured. In many studies a general scale is used whereas in Blackmore’s 1997 study there was simply one question about whether the participant believed in ESP.

AO2 Probability judgement Correlation isn’t a cause – The research evidence largely suggests that there is a link between probability misjudgement and paranormal beliefs, but such a link doesn’t mean we are justified in concluding that difficulties in making appropriate probability judgements cause the paranormal beliefs. There may be an intervening factor, such as cognitive ability.

AO2 Probability judgement Cognitive ability – Cognitive ability may explain the link between probability misjudgement and paranormal beliefs. Musch and Ehrenberg (2002) controlled for differences in general cognitive ability and found this reduced the performance difference between believers and nonbelievers on probability judgement tasks to zero. So it may be that poor probability judgements are due to low cognitive ability and not a component in paranormal belief (though research discussed above suggests this is unlikely).

AO2 Probability judgement Not misjudgement, simply a different heuristic – A different approach to probability misjudgement is offered by Kahneman and Tversky (1972). They suggest that people use various heuristics (strategies to solve problems), such as representativeness. For example, some people understand that short runs of tossing a coin will not be representative of a theoretical probability of 50:50 whereas other people expect short runs to match theoretical probability. This is referred to as the gambler’s fallacy, for example, believing that if you throw a coin and get three heads in succession it is more likely that tails will come up next (it isn’t – the probability remains the same).

Exam question Discuss the role of probability judgement in anomalous beliefs (4 + 6)