6.1 INTRODUCTION
The results of the previous experiment indicated that hindsight bias may not be a particularly strong or consistent phenomenon. One reason for this was that two variables were found to affect it, firstly, it may be mediated by the position of outcome knowledge in relation to the event description. Secondly, certain information orders may act to reduce or encourage it. In contrast to the previous experiment the one to be reported here investigated creeping determinism rathern than hindsight bias.
There are two reasons for this. Firstly, the lack of strong support for hindsight bias makes it of interest to attempt to replicate Fischhoff's (1975a) results with respect to creeping determinism. Secondly, as Fischhoff (1975a) reports, creeping determinism to
be a stronger phenomenon than hindsight bias we may be able to determine more precisely the effects of position of outcome knowledge and
information order.
It will be recalled from Chapter 3 that a distinction was made between creeping determinism and hindsight bias. The latter was said to occur only when subjects were given instructions which, either explicitly or implicitly, asked them to ignore outcome knowledge
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CHAPTER 6.
EXPERIMENT 2: POSITION OF OUTCOME KNOWLEDGE AND HINDSIGHT JUDGEMENTS
6.1 INTRODUCTION
The results of the previous experiment indicated that hindsight bias may not be a particularly strong or consistent phenomenon. One reason for this was that two variables were found to affect it, firstly, it may be mediated by the position of outcome knowledge in relation to the event description. Secondly, certain information orders may act to reduce or encourage it. In contrast to the previous experiment the one to be reported here investigated creeping determinism rathern than hindsight bias.
There are two reasons for this. Firstly, the lack of strong support for hindsight bias makes it of interest to attempt to replicate Fischhoff's (1975a) results w i t h respect to creeping determinism. Secondly, as Fischhoff (1975a) reports, creeping determinism to
be a stronger phenomenon than hindsight bias we may be able to determine more precisely the effects of position of outcome knowledge and
information order.
It will be recalled from Chapter 3 that a distinction was made between creeping determinism and hindsight bias. The latter was said to occur only when subjects we r e given instructions which, either explicitly or implicitly, asked them to ignore outcome knowledge
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(i.e. attempt to reconstruct a foresight state) when making judgements. Creeping determinism, on the other hand, was said to occur when
subjects, provided with outcome knowledge and an event description, were asked to make judgements in the light of all the information they had been given. Fischhoff (1975a) finds creeping determinism to be a stronger phenomenon than hindsight bias. For example, pooling his results from Tables 1 and 3 (pp. 293 and 295 respectively) for the outcome reported to have occurred we find that the median foresight/ hindsight difference is 14.2% and 9.5% for creeping determinism and hindsight bias respectively.
The experiment to be reported here investigated three hypotheses:
that creeping determinism would (1) be more in evidence when outcome
knowledge was given after the event description than before; (2)
that confidence in the judgements made by subjects would be greater in hindsight than foresight; (3) that information appearing last which indicates that the reported outcome will occur will have a stronger influence on judgements than information which appeared first.
The first hypothesis is an extension of the indications in the, previous experiment that outcome knowledge given at the end of an event description may induce greater hindsight bias than if it were given at the beginning. The hypothesis is lent further credence by the recency effects reported in the previous experiment. If subjects are instructed to make judgements in the light of all information, as in those for creeping determinism, the existence of recency
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when outcome knowledge is given last rather than first.
The second hypothesis also derives from Fischhoff's general finding that outcome knowledge leads people to perceive that outcome
as more inevitable than if they did not know the outcome. This is
so because it follows from this that we would expect people to feel more confident in their judgements in hindsight. Indirect support for this hypothesis can be found in a number of historical writings. For example, Wohlsletter (1962) comments:
" . . . it is much easier after the event to sort out the relevant from the irrelevant signals. After the event, of course, a signal is always crystal clear; we can now see what disaster it was signalling, since the disaster has occurred." (p. 387)
The third hypothesis is made as a result of the findings in the previous experiment, where, as discussed above, recency effects were
found. There is no obvious reason why this should not apply when creeping determinism rather than hindsight bias is being investigated.
The experiment to be reported here loses the same scenarios and out- I comes as in the previous one. It differs in that subjects were pre sented with continuous prose passages rather than the sequential presentation of information method. This was done because of the
focus upon replication and extension of Fischhoff (1975a). Consequently
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6.2. METHOD SUBJECTS
120 undergraduate students at the University of Warwick acted as subjects in this experiment.
PROCEDURE
40 subjects were randomly assigned to a Foresight (F) condition: 40 to a hindsight condition (HB) in which they were told what happened before reading the event description (this is equivalent to the H2
condition in Experiment 1); and 40 to a hindsight condition (HA) in which they were told the outcome after reading the details of the scenario. In each condition subjects read one (and only one) of the four scenarios used in Experiment 1. Subjects in all conditions were asked to make two sets of judgements, first to assess the likelihood (in percentage form) of each of the possible outcomes specified to a scenario;
secondly, to indicate how confident they felt about their assessments. They did this on a scale where O was "unsure" and 5 was "very confident". Likelihood assessments, as in Experiment 1, given to the four possible outcomes of a scenario had to add up to 100%.
INSTRUCTIONS
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