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The base rate fallacy, also called base rate neglect, is an error that occurs when the conditional probability of some hypothesis H given some evidence E is assessed without taking sufficient account of the "base rate" or "prior probability" of H.

Example

In a city with 100 terrorists and one million non-terrorists there is a surveillance camera with an automatic face recognition software. If the camera sees a known terrorist, it will ring a bell with 99% probability. If the camera sees a non-terrorist, it will trigger the alarm 1% of the time. So, the failure rate of the camera is always 1%.

Suppose somebody triggers the alarm. What is the chance he/she is really a terrorist?

Imagine that all 1,000,100 people pass in front of the camera. About 99 of the 100 terrorists will trigger a ring — and so will about 10,000 of the million of nonterrorists. Therefore 10099 people will be rung at, and only 99 of them are terrorists. So, the probability that a person who triggers the alarm is actually a terrorist is 99 in 10,099 (about 1/100).

Someone making the base rate fallacy, instead of running the numbers as above, would just claim that, as the failure rate of the device is 1 in 100, then the false alarm rate must be 1 in 100 as well, and so, if the device rings at anyone, he/she is 99% sure to be a terrorist, and should be shot at.

The base rate fallacy is only fallacious when non-terrorists outnumber terrorists, or conversely. In a city with about 50% terrorists and about 50% nonterrorists, the real probability of misidentification won't be far from the failure rate of the device.

Findings in psychology

In some experiments, students were asked to estimate the grade point averages (GPAs) of hypothetical students. When given relevant statistics about GPA distribution, students tended to ignore them if given descriptive information about the particular student, even if the new descriptive information was obviously of little or no relevance to school performance. This finding has been used to argue that interviews are an unnecessary part of the college admissions process because interviewers are unable to pick successful candidates better than basic statistics^[who?].

Psychologists Daniel Kahneman and Amos Tversky attempted to explain this finding in terms of the representativeness heuristic. Richard Nisbett has argued that some attributional biases like the fundamental attribution error are instances of the base rate fallacy: people underutilize "consensus information" (the "base rate") about how others behaved in similar situations and instead prefer simpler dispositional attributions.

References

Bar-Hillel, M. (1980). The base-rate fallacy in probability judgments. Acta Psychologica, 44, 211-233.
Kahneman, D., & Tversky, A. (1973). On the psychology of prediction. Psychological Review, 80, 237-251. (summary here)
Nisbett, R. E., Borgida, E., Crandall, R., & Reed, H. (1976). Popular induction: Information is not always informative. In J. S. Carroll & J. W. Payne (Eds.), Cognition and social behavior, 2, 227-236.

External links

Psychology of Intelligence Analysis: Base Rate Fallacy

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+The '''base rate fallacy''', also called '''base rate neglect''', is an error that occurs when the [[conditional probability]] of some hypothesis H given some evidence E is assessed without taking sufficient account of the "[[base rate]]" or "[[prior probability]]" of H.
-Locarno Pan,
+===Example===
+In a city with 100 terrorists and one million non-terrorists there is a surveillance camera with an automatic face recognition software. If the camera sees a known terrorist, it will ring a bell with 99% probability. If the camera sees a non-terrorist, it will trigger the alarm 1% of the time. So, the failure rate of the camera is always 1%.
+Suppose somebody triggers the alarm. What is the chance he/she is really a terrorist?
-The First and the only ultimate creature in this world.
+Imagine that all 1,000,100 people pass in front of the camera. About 99 of the 100 terrorists will trigger a ring — and so will about 10,000 of the million of nonterrorists. Therefore 10099 people will be rung at, and only 99 of them are terrorists. So, the probability that a person who triggers the alarm is actually a terrorist is 99 in 10,099 (about 1/100).
-Born in 1981, the Aug 8th, been raised in Taipei, Taiwan.
+Someone making the base rate fallacy, instead of running the numbers as above, would just claim that, as the failure rate of the device is 1 in 100, then the false alarm rate must be 1 in 100 as well, and so, if the device rings at anyone, he/she is 99% sure to be a terrorist, and should be shot at.
-Now is looking for the long term team members in the same interests and goals to make the world better.
+The base rate fallacy is only fallacious when non-terrorists outnumber terrorists, or conversely. In a  city with about 50% terrorists and about 50% nonterrorists, the real probability of misidentification won't be far from the  failure rate of the device.
-Personally, I believe that "group wisdom" is more powerful than the single. Internet is a world-wide tool that connects everyone in a whole.
+== Findings in psychology ==
-Starts on Today and see what's going on next.
+In some experiments, students were asked to estimate the [[grade point average]]s (GPAs) of hypothetical students. When given relevant statistics about GPA distribution, students tended to ignore them if given descriptive information about the particular student, even if the new descriptive information was obviously of little or no relevance to school performance. This finding has been used to argue that interviews are an unnecessary part of the [[college admissions]] process because interviewers are unable to pick successful candidates better than basic statistics{{who}}.
-Biography:
+[[Psychologist]]s [[Daniel Kahneman]] and [[Amos Tversky]] attempted to explain this finding in terms of the [[representativeness heuristic]]. [[Richard Nisbett]] has argued that some [[attributional bias]]es like the [[fundamental attribution error]] are instances of the base rate fallacy: people underutilize "consensus information" (the "base rate") about how others behaved in similar situations and instead prefer simpler [[dispositional attribution]]s.
-.Past
+== See also ==
-.Present
+* [[Bayesian probability]]
+* [[Inductive argument]]
+* [[Misleading vividness]]
+* [[Data dredging]]
+==References==
-.Future
+* [http://dx.doi.org/10.1016/0001-6918(80)90046-3 Bar-Hillel, M. (1980). The base-rate fallacy in probability judgments.  ''Acta Psychologica'', 44, 211-233.]
-Career Achievements:
+* Kahneman, D., & Tversky, A. (1973). On the psychology of prediction. ''Psychological Review'', 80, 237-251. ([http://faculty.babson.edu/krollag/org_site/soc_psych/kan_tver_pred.html summary here])
+* Nisbett, R. E., Borgida, E., Crandall, R., & Reed, H. (1976).  Popular induction: Information is not always informative. In J. S. Carroll & J. W. Payne (Eds.), ''Cognition and social behavior'', 2, 227-236.
+==External links==
-Objective
-To become multi-cultural future employee for the fast moving trend, willing to take challenges, make huge profits and integrate the resource to somehow do good for the society. Although theatre is my profession , fast and strong motivation of passion to learn is my excellence to challenge different field.
-Advantage of Personality
-. Both soft and tough to face different situation
-. Modest but willing to take challenge when it needed
-. Nice talking and easily to get along with；I know good & bad
-   part of myself
-. Calm and ability to judge when face difficulties
-. Curiosity for a lot of things, especially for global
-   trends
-Disadvantage of Personality
-. Aloof and silent sometimes, due to needing some private
-   space to think
-. Sensitivity；Sometimes is good, sometimes it would cause a
-   little blue temper
-. Stubborn；I do what I believe in, Endless to find what is
-   right.
-. At the beginning, lack of self-confidence, I need time and
-   courage to prove myself
-. Capacity of accepting failure is still not as well as I
-   expect
+* [https://www.cia.gov/library/center-for-the-study-of-intelligence/csi-publications/books-and-monographs/psychology-of-intelligence-analysis/art15.html#ft145 Psychology of Intelligence Analysis: Base Rate Fallacy]
-Education
-Taipei National University of the Arts-BFA
-Young-Ming high school
-Libby high school, MT U.S.A.-Exchange Program
+{{Relevance fallacies}}
-Life & Work Experience
-Strong background of multi-culture Experienced
+[[Category:Relevance fallacies]]
-‧Joint Force Tech co, Ltd. Sales Representatives &
+[[Category:Cognitive biases]]
-        Secretary
+[[Category:Behavioral finance]]
-‧Received the “Most Dedicating Corporal in WPN Company
-        Certificate”
+[[fr:Oubli de la fréquence de base]]
-‧Graduated from Taipei National University of the Arts,
+[[he:כשל הסתברות קודמת]]
-        majored in Stage Management
+[[pl:Zaniedbywanie miarodajności]]
-      ‧Serving as R.O.C. military Corporal
-‧I-Wan-Jan Puppet Troupe/White Dance Troupe【The HongNi
-        Pass】-Stage Manager
-      ‧Performance Workshop Theatre/TNUA【A Dream Like A
-        Dream】；Directed by Stan Lai-ASM
-      ‧TNUA Graduation Assembly –Stage Manager
-      ‧Tan Theatre【Fat is good】- Stage Manager
-      ‧The 7th  Taipei Arts Festival【Oriental Avant-Grade】
-        Opening Ceremony- Stage Manager
-      ‧The 7th  Taipei Arts Festival【Playing inside & outside
-        together】-Stage Manager
-      ‧TNUA Graduate Production【Harvey】-Stage Manager
-      ‧Shakespeare’s Wild Sisters Grope【A Hundred Year of
-        Solitude】- Stage Manager
-      ‧TNUA School Production【Romeo & Juliet】；Directed by
-        Daniel S.P Young -Stage Manager
-      ‧Experience for several Taiwan Theatre Company as
-        Lighting & Set Crew.
-‧TNUA Performance Ⅲ【Gas Heart】-Ear
-       【Dans la solitude des champs de coton】-Merchant
-      ‧TNUA Production【Who’s afraid of Virginia Wolf】-Stage
-        Manager
-      ‧Taiwan Walker Theatre【Taipei Tour】-ASM
-      ‧Spring Wind Theatre【A Midnight summer’s dream】-ASM
-      ‧TNUA production【The Increased Difficulty of
-        Concentration】-Stage Manager
-‧TNUA Production【Metamorphosis】- ASM
-      ‧TNUA Graduate Production【Chinese Opera : Monkey King】
-        -Stage Manager
-      ‧CITYSTORYTHEATRE【Suburban Motel】-Stage Manager
-      ‧TNUA Graduate Production【Die Zeit und das Zimmer】-
-        Frank
-‧TNUA Graduate Production【Henry the fourth in Puppet】
-        -Puppet player
-      ‧Represented I-Wan-Jan Puppet Troupe to perform in
-        International Puppet Festival in Republic of Moldova
-      ‧EF Exchange Program Summer Camp- Returnee
-      ‧Spring-Sun Theatre【What’s Love About】-Rehearsal
-        assistant.
-‧Taipei National University of the Arts, theatre Dep.
-        Freshman
-      ‧Shang Orientheatre -Actor
-      ‧White Dance Troupe -Actor, Puppet Player
-‧Graduated from Libby High School, Montana.
-      ‧Perform “Chinese Hand Puppet” in The Universal School,
-        Varanasi , India
-‧Represented Overseas Compatriot Affair Commission
-        R.O.C. to perform
-        Chinese Hand Puppet with I-Wan-Jan Puppet Troupe.
-      ‧EF Program Exchange Student
-      ‧Represented Libby High School to compete in Montana
-        State Speech & Drama Contest, winning 8th place in
-        Pantomime.1998  ‧Represented Young-Ming high school to
-        Singapore for short-term Exchange Program
-‧Perform “Chinese Hand Puppet” in Korea International
-        Puppet Festival in CHUNCHEON
-‧Study “Chinese Hand Puppet” from Puppet Master Lee,
-        Ten-Lu