# The effects of monetary incentives on how conjunctive probabilities are assessed

- Hakan Nilsson,
*University of Basel*
- Jörg Rieskamp,
*University of Basel*

## Abstract

This paper explores how people compute conjunctive probabilities
when monetary incentives are present. In E1, participants encounter urns filled
with 100 balls among which n are colored. Participants learn about the n of
colored balls by observing balls being sampled. At test, people encounter
questions like “two balls will be drawn, one from the black urn and one from
the blue urn, what is the probability that one is black and one is blue?”.
Payment is based on a proper scoring-rule rewarding participants that estimate
probabilities that correspond with the underlying true probabilities. By modeling
how people combine single event probabilities (one ball is black) into
conjunctive event probabilities (one ball is black and one is blue) we show that
people estimate conjunctive probabilities by taking a weighted average between
single event probabilities. E2 show similar results when the test task is to
choose between options in a gamble.

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