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When 90% confidence intervals are 50% certain: on the credibility of credible intervals
Author(s) -
Teigen Karl Halvor,
JØrgensen Magne
Publication year - 2005
Publication title -
applied cognitive psychology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.719
H-Index - 100
eISSN - 1099-0720
pISSN - 0888-4080
DOI - 10.1002/acp.1085
Subject(s) - overconfidence effect , confidence interval , robust confidence intervals , credible interval , credibility , statistics , tolerance interval , psychology , confidence distribution , cdf based nonparametric confidence interval , range (aeronautics) , econometrics , mathematics , social psychology , materials science , political science , law , composite material
Abstract Estimated confidence intervals for general knowledge items are usually too narrow. We report five experiments showing that people have much less confidence in these intervals than dictated by the assigned level of confidence. For instance, 90% intervals can be associated with an estimated confidence of 50% or less (and still lower hit rates). Moreover, interval width appears to remain stable over a wide range of instructions (high and low numeric and verbal confidence levels). This leads to a high degree of overconfidence for 90% intervals, but less for 50% intervals or for free choice intervals (without an assigned degree of confidence). To increase interval width one may have to ask exclusion rather than inclusion questions, for instance by soliciting ‘improbable’ upper and lower values (Experiment 4), or by asking separate ‘more than’ and ‘less than’ questions (Experiment 5). We conclude that interval width and degree of confidence have different determinants, and cannot be regarded as equivalent ways of expressing uncertainty. Copyright © 2005 John Wiley & Sons, Ltd.