Graphs versus numbers : How information format affects risk aversion in gambling

Abstract

In lottery gambling, the common phenomenon of risk aversion shows up as preference of the option with the higher win probability, even if a riskier alternative offers a greater expected value. Because riskier choices would optimize profitability in such cases, the present study investigates the visual format, with which lotteries are conveyed, as potential instrument to modulate risk attitudes. Previous research has shown that enhanced attention to graphical compared to numerical probabilities can increase risk aversion, but evidence for the reverse effect — reduced risk aversion through a graphical display of outcomes — is sparse. We conducted three experiments, in which participants repeatedly selected one of two lotteries. Probabilities and outcomes were either presented numerically or in a graphical format that consisted of pie charts (Experiment 1) or icon arrays (Experiment 2 and 3). Further, expected values were either higher in the safer or in the riskier lottery, or they did not differ between the options. Despite a marked risk aversion in all experiments, our results show that presenting outcomes as graphs can reduce — albeit not eliminate — risk aversion (Experiment 3). Yet, not all formats prove suitable, and non-intuitive outcome graphs can even enhance risk aversion (Experiment 1). Joint analyses of choice proportions and response times (RTs) further uncovered that risk aversion leads to safe choices particularly in fast decisions. This pattern is expressed under graphical probabilities, whereas graphical outcomes can weaken the rapid dominance of risk aversion and the variability over RTs (Experiment 1 and 2). Together, our findings demonstrate the relevance of information format for risky decisions.