When we wrongly judge the conjunction of two events to be more likely than one of the events, when compared directly. A conjunction is the joining of two statements with words like 'and'.
Example:
Scenario 1: Bob cares about his fitness and health.
Scenario 2: Bob cares about his fitness and health, and runs frequently.
The conjunction fallacy occurs when we deem Scenario 2 to be more likely than Scenario 1, even though logically this cannot be the case (since Scenario 1 includes Scenario 2).
Definition: When people judge the conjunction of two events to be more probable than one of the events in a direct comparison.
Example: The Linda Problem. 'Linda is thirty-one years old, single, outspoken, and very bright. She majored in philosophy. As a student, she was deeply concerned with issues of discrimination and social justice, and also participated in antinuclear demonstrations... Which alternative is more probable?
Linda is a bank teller.
Linda is a bank teller and is active in the feminist movement...About 85% to 90% of undergraduates at several major universities chose the second option, contrary to logic.'
Insight: Greater detail means less probability.
Insight: We are drawn quickly to stories that seem plausible, using representativeness.
Insight: Information overload can hinder our ability to make sound judgements.
Insight: Considering the few important factors can lead to more effective decision making.
Insight: More variables to consider in decision making makes it more likely that we give more weight to unimportant variables, and less weight to important ones.
Reference: Kaheman and Tversky in naming the Conjunction Fallacy.
Insight: People often believe that scenarios with more detail are more likely because of "representativeness" (plausibility because of similarities with other subsets).
Example: Lawyers could effectively make something more believable with more details, even though the additional details make the scenario less likely.
Reference: The Linda Problem: Kahneman and Tversky.
Reference: Seven letter words ending in "ing" vs seven letter words with "n" in the sixth position: Kahneman and Tversky.
Definition: When a subset seems larger than a set.
Insight: We easily fall for this fallacy because we are attracted to plausible stories.
Insight: Additional conditions means that something is always less likely.
Insight: It is not logically possible for two events to be more likely than one alone.
Reference: The Linda Problem: Kahneman and Tversky.
Key Insights & Principles
Decision Making
More variables = less likely.
We are drawn to believe that more details in stories makes them more plausible.
More information often hinders our ability to clearly see that which is important to decision making.
The consideration of more variables in decision making makes us more likely to attach greater meaning or weight to unimportant details, and less weight to important ones.
When making decisions focus on the few important details.
