The effect of probability and framing on the default effect in decision making under risk.

This study examines how probability and outcome framing modulate the default effect in risky decision-making using two controlled experiments with probabilistically equivalent lotteries. Participants repeatedly chose among four equivalent betting options, with one highlighted as a default. Across both studies (N = 317), we document a robust default effect, with 38-39% choosing defaults versus a 25% random benchmark. Crucially, low winning probability (25% vs. 75%) consistently amplified default reliance. However, loss framing increased default choices significantly only in Study 1 (where task descriptions differed across probabilities) but not in Study 2 (where task framing was standardized). This suggests winning probability is a more reliable moderator than framing. Post-experiment surveys indicate cognitive ease and responsibility avoidance are key psychological mechanisms: low probability heightens the difficulty of winning, increasing default acceptance, while loss framing exacerbates responsibility aversion. The study advances understanding of the economic and contextual determinants of the default effect and highlights its implications for designing choice architectures in real-world applications where uncertainty is prominent.