Tendency for people to ignore causally-relevant base rates in favor of individuating information.
Tversky, A., & Kahneman, D. (1982). Evidential impact of base rates. In Kahneman, D., Slovic, P., & Tversky, A. (Eds.), Judgment under uncertainty: Heuristics and biases (pp. 153–160) Cambridge: Cambridge University Press.
Participants are provided with two conflicting pieces of information: one is statistical and favors one decision (e.g., "The probability of winning a lottery ticket is 10%") while another is based on personal, case-based experience and favors another decision (e.g., "John, who was wearing his lucky shirt and who had found a four-leaf clover that day, decided to buy one lottery ticket"). Participants are required to choose between four possible answers: two indicating reliance on the base rate and two indicating reliance on the personal information.
1. As the Chief Financial Officer of a corporation, you are planning to buy new laptops for the workers of the company. Today, you have to choose between two types of laptops that are almost identical with regard to price and the most important capabilities. According to statistics from trusted sources, type “A” is much more reliable than type “B”. One of your acquaintances, however, tells you that the motherboard of the type “A” laptop he bought burnt out within a month and he lost a significant amount of data. As for type “B”, none of your acquaintances have experienced any problems. You do not have time for gathering more information.
Which type of laptop will you buy?
a) Definitely type A
b) Probably type A
c) Probably type B
d) Definitely type B
2. Professor Kellan, the director of a teacher preparation program, was designing a new course in human development and needed to select a textbook for the new course. She had narrowed her decision down to one of two textbooks: one published by Pearson and the other published by McGraw. Professor Kellan belonged to several professional organizations that provided Web-based forums for its members to share information about curricular issues. Each of the forums had a textbook evaluation section, and the websites unanimously rated the McGraw textbook as the better choice in every category rated. Categories evaluated included quality of the writing, among others. Just before Professor Kellan was about to place the order for the McGraw book, however, she asked an experienced colleague for her opinion about the textbooks. Her colleague reported that she preferred the Pearson book.
What do you think Professor Kellan should do?
a) Should definitely use the Pearson textbook (1 point)
b) Should probably use the Pearson textbook (2 points)
c) Should probably use the McGraw textbook (3 points)
d) Should definitely use the McGraw textbook (4 points)
3. The Caldwells had long ago decided that when it was time to replace their car they would get what they called "one of those solid, safety-conscious, built-to-last Swedish" cars -- either a Volvo or a Saab. When the time to buy came, the Caldwells found that both Volvos and Saabs were expensive, but they decided to stick with their decision and to do some research on whether to buy a Volvo or a Saab. They got a copy of Consumer Reports and there they found that the consensus of the experts was that both cars were very sound mechanically, although the Volvo was felt to be slightly superior on some dimensions. They also found that the readers of Consumer Reports who owned a Volvo reported having somewhat fewer mechanical problems than owners of Saabs. They were about to go and strike a bargain with the Volvo dealer when Mr. Caldwell remembered that they had two friends who owned a Saab and one who owned a Volvo. Mr. Caldwell called up the friends. Both Saab owners reported having had a few mechanical problems but nothing major. The Volvo owner exploded when asked how he liked his car. "First that fancy fuel injection computer thing went out: $400 bucks. Next, I started having trouble with the rear end. Had to replace it. Then the transmission and the brakes. I finally sold it after 3 years at a big loss."
What do you think the Caldwells should do?
a) They should definitely buy the Saab
b) They should probably buy the Saab
c) They should probably buy the Volvo
d) They should definitely buy the Volvo
Each option is associated with a given number of points and the total score is the average of the responses.
Erceg, N., Galić, Z., & Bubić, A. (2022). Normative responding on cognitive bias tasks: Some evidence for a weak rationality factor that is mostly explained by numeracy and actively open-minded thinking. Intelligence, 90, 101619.