Lecture 3: Making Likelihood Judgements Flashcards
Uncertainty
Statistical Definition
The probability of an event occurring is not equal to 0 or 1
Likelihood judgement
judgment of how probable an event is to occur or how likely a statement is to be true
Heuristic
- systematic
- quick to use
- easy to use
- used under conditions of
uncertainty - simplifies the procedure for obtaining a probability
- reduces the complexity of obtaining a probability
Tversky and Kahneman (1973)
Do people use the availability heuristic when estimating frequencies?
People use the availability heuristic when estimating frequencies
Availability Heuristic
“People assess the frequency of a class or the probability of an event by the ease with which instances or occurrences can be brought to mind” (Tversky & Kahneman, 1974, p 1127)
Judge the size of a set/frequency of events
normative - how many items/events
Descriptive - use rule: how many items, events can be easily recalled
Method: Relative Frequency-of-Occurrence Judgement
- Participants given or asked to generate lists of two possible events or items
- Participants asked to determine which item or event occurs more frequently
Result of Relative Frequency-of-Occurrence Judgement
For the consonants K, L, N, R, V:
“Among the 152 subjects, 105 judged the first position to be more likely for a majority of the letters, and 47 judged the third position to be more likely for a majority of the letters.”
(Tversky & Kahneman, 1973, p211-212)
The reality; there are more words where these letters appear in the third position
Tversky and Kahneman (1973)
Do people use the availability heuristic to estimate frequencies when the actual frequencies are presented?
When people estimate frequencies based on available information, people use availability heuristic
Method: Set-Size Judgement
Participants asked to estimate the number of items in the set or class
Result of Set-Size Judgement
“Among the 99 subjects who compared the
frequency of men and women in the lists, 80 erroneously judged the class consisting of the more famous names to be more frequent”
(Tversky & Kahneman, 1973, p221)
Finding Interpretation of Set-Size Judgement
“people judge the frequency of a class by assessed availability, i.e., by the ease with which the relevant instances come to mind.”
The availbility heuristic in clinical decision making
Do clinicians make use of the availability heuristic when making diagnoses?
The law of small numbers
the tendency to think of small samples that appear random are representative of the population
Kahneman and Tversky (1973)
Do people use the representativeness heuristic?
- people use the representativeness heuristic
- as a consequence people commit the base rate fallacy
