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Flashcards in SPRING Reasoning and judgement Deck (33):

describe the sally clarke problem

both babies die from sudden infant death - very unlikely
argued that prob so low, more likely to be murder
but lawyers used poor statistical reasoning - two events were not independent of eachother and the prob of two independent events not the same as two linked ones (prosecutors fallacy)
ignores probabilities of two murders in same family


contraceptive probabiities

98% vs 99% effective
over time, 98% sig less effective than 99%


how do we make subjective probability judgements

decision making based on SEU
heuristic strategies to judge the likelihood of event occurance


describe the availability heuristic

judge probability based on ease comes to mind
if more freq then more available


tversky and kahenman availability heuristic

more common: r as first or third letter
most say first - easier to think of words beginning with r


slovic, fichoff and litchenstien 1979 availability heurostic

estimate freq of causes of death
overestimate those unlikely but heavily reported ie murder and underestimate those rarely reported ie emphysema


describe the representativeness heuristic

degree of correspondence between an instance and a category
ie looks and sounds like it so probably is
how much a certain set of circumstances will drive the likelihood of something based on past experience - link closely to stereotypes


tversky and kahenmen 1983 conjunction fallacy (representativeness heuristic)

liinda - bank teller, feminist bank teller, feminist
often chose feminist bank teller but statistically the least likely
two independent events make conjunction of two together even less probable - feminist bankteller is smaller subset of banktellers


describe anchoring heuristic

base estimated probability on the first piece of information we are given


tversky and kahenman 1974 anchoring

estimates under time pressure
1. 1x2x3x4x5x6x7...
2. 7x6x5x4x3x2x1
= ~40000
BUT estimate 1 lower than 2 based on first numbers


lichtenstein et al 1978 anchoring

achoring on first given value means fail to adjust appropriately
estimate freq of 40 causes of death
a. 50000 motor cycle or b.10000 electrocution
estimate higher for a


real world examples of anchoring

anchoring consumers for price reference so view as less expensive
credit card minimums
high prices as ref point for lower


what is bayesian reasoning

update probabilities based on additional information that causes to ignore the original base rate and focus on hit rate
make probabalistic inferences based on additional info and therefore forget the initial info given


kahenman and tversky 1973 base rate fallacy

30 engineers and 70 lawyers
stereotypical description of engineer/lawyer or neutral
neurtral tend to report 50%
rate increase if stereotypical


medical diagnosis problem base rate fallacy
casscells et al 1978

prob breast cancer 1%...given values of pos mamog if have cancer = 80% and not = 9.6%
= overall 7.8% prob
clinicians probability = 70-80% as ignore probability of 1% and focus on hit rate


gigerenzer, hofferage and ebert 1998 bayesian reasoning

positive HIV test - prob that ACUTALLY positive?
clinicians say 100% even if low risk patient


gigerenzer and hofferage 1995 format of decision

if way info is presented is more reflective of the way we make decisions in real life then more likely to interpret in correct way
ie breast cancer problem in frequency format and most people get correct


cosmides and tooby 1996frequentists hypothesis
why are frequency problems easier

inductive readoning = prob in the form of freq
easier to break down if in freuqncy form - tree


girotto and gonzalez 2001 defective frequencies

if not given enough info to complete freq tree OR the information given is all drawn from multiple samples


how might you improve bayesian reasoning problems

change structure of the info not the format
apply cumulative reasoning


what are naive probabilites

when people make judgements on probabilities they are not expert in - relate to the alternatives they consider
ie not given probabilties then assume equiprobable


girotto and gonzalez 2001 prob and freq use

prob not alwats bad ie can format as chance to improve interpretation
freq not alwats good - come harder than probabilities, dependent on the info structure


mccloy byrne and johnson laurd 2010 improveing bayesian readoning

naive individuals dont use binomal formula to calc cumulative prob and instead use conjunctions ie if not yet occred then the prob = 0/no. trials
those who recog that freq cumulates over time may still underestimate the rate of increased risk
improve by presenting problems in specific ways - ie more structured layout


johnson laird et al
sentanial resoning

when an individual understands discours and imagines a state of affairs then constructs mental models of the relevant situation
prepresents the possibilities and diff ways they might occur - represents explicitly what is true but not what is false
each model therefore represents an equiprobable alt unless info given to hold belief of the contrary
the greater the no of mental models a task elicits and the greater their complexity the worse the performance


equiprobable sentenial reasoning example

box with red or black marble or both
prob of black marble with another marble?
- tend to say 2/3 as no info given about prob - ill specified


define prosecutors fallacy

tendency to ignore that to occurances are not statistically independent from one another and therefore the probability of the two occuring is lower (more likely) than if they were independent


how did sally clarkes case fail to prosecutors fallacy

argued deaths of two newborns statistically independent = 1/72m and that this equates to the prob that guilty
BUT NOT - sig lower prob because share same environment


define bayesian reasoning

a means of quantifying uncertainty
rule for refining an hypothesis by factoring in additional evidence and background information, and leads to a number representing the degree of probability that the hypothesis is true
- ie accounting for independence of events in prosecutors fallacy


define subjective probability

the extent to which a coherent person believes that a statement is true based on the info that is available at that time
use of heuristics to form a subjective judgement


seidelmeier hertwig and gigerenzer 1998
availability heiristic

memory often good at stoing freq info
tend to measure ease info comes to mind based on no instances retrieved in given time frame and speed of retrieval
BUT - some predictions where overestimate low freq and underestimate high so not always completely accurate


describe linda
t+k conjunction fallacy

31 y/o outspoken and bright
major in philosophy
concerned with discrimination and social justice
participates in antinuclear demonstrations


diff subective prob judgements

availability heuristic
representativeness heuristic


bayesian reasoning prob

base rate fallacy
medical diagnosis prob
hiv screening
prob vs freq vs chance