Default Bias and Coin-flipping

Participants complete binary lottery choice tasks over seven sessions, each on a separate day.

In Sessions 1–6 (Treatment Sessions), participants complete tasks under each of the six conditions, one condition per session, in a randomized order. In the benchmark condition (C0), participants directly choose between two lotteries. In the default condition (C1), one lottery is randomly assigned as the default, and the participant decides whether to keep it or switch. In the delegation condition (C2), participants may choose a lottery directly or delegate the decision to a fair coin flip. In the advice condition (C3), participants may choose directly or request a random assignment that they can then keep or switch. In the default–delegation condition (C4), one lottery is randomly assigned as the default, and the participant decides whether to keep it, switch to the other lottery, or delegate the decision to a fair coin flip. In the default–advice condition (C5), one lottery is randomly assigned as the default, and the participant decides whether to keep it, switch to the other lottery, or request a randomized recommendation that can then be accepted or rejected.

In Session 7 (Elicitation Session), participants make direct choices only, with each choice presented twice.

2026-05-25

2026-07-31

The primary outcomes are (i) whether the participant accepts or switches away from an assigned default (in conditions with defaults: C1, C4, C5); (ii) whether the participant delegates the decision to the random device (in delegation conditions: C2, C4); (iii) whether the participant seeks randomized advice and accepts the advice after receiving a randomly assigned lottery (in advice conditions: C3, C5).

Secondary outcomes include measures of (i) choice variability; (ii) choice heterogeneity; (iii) violations of transitivity; and (iv) response times, measured at the choice level and/or the participant level using Elicitation Session data.

This is a within-subject experiment with six treatment conditions. Participants complete Sessions 1–6 under each of the six conditions (64 choices per session), with condition order randomized across participants. Session 7 is the Elicitation Session, consisting of 128 binary lottery choices under the benchmark (direct choice) condition, with each choice set repeated to allow measurement of choice stochasticity. Participants complete each session on a separate day.

Each lottery pair consists of two lotteries with four equiprobable monetary outcomes. Lottery pairs are drawn from 16 parameterized choice sets grouped into three categories: (1) "hard" choices where lotteries have equal expected values but differ in dispersion; (2) epsilon-perturbed repetitions of hard choices with small expected value differences; and (3) "easy" choices where one lottery has a clearly higher expected value. Choice set parameters are randomly generated within pre-specified ranges.

Participants share some choice sets across conditions (for cross-condition comparisons) and face some choice sets unique to each condition (to reduce perceived repetition). At the end of the experiment, one decision is randomly selected for payment.

Not available

The order of conditions in Sessions 1–6 is randomized at the individual participant level. Within each session, the order of choice tasks is also randomized at the participant level. The presentation order of the two lotteries is randomized at the participant–choice level. All within-task random assignments (defaults and coin flips) use fair randomization with equal probability. Randomization is implemented by the experimental software.

Individual participant. All conditions are within-subject; randomization of condition order and within-task assignments occurs at the individual level.

No

The target analysis sample is 500 participants who complete all experimental sessions. Because participation requires completing multiple sessions, some attrition is expected due to participants failing to complete all sessions. We anticipate an attrition rate of approximately 5–10%. To achieve the target analysis sample of 500 participants, approximately 550 participants will be recruited initially. Participants who do not complete all sessions will be excluded from the main analysis sample.

Around 500 * 512 = 256,000 (number of participants × number of choice tasks per participant). All participants complete all six conditions (within-subject design). Each participant makes 64 decisions per treatment condition in Sessions 1–6 and 128 decisions in the Elicitation Session (Session 7), for a total of 512 decisions per participant.

Around 500 * 64 = 32,000 (number of participants × number of choice tasks per participant).
Each participant makes 64 decisions per treatment condition.

Given 500 participants making 64 choices each per treatment condition, the study is highly powered to detect even small effects of random defaults, delegation to a random device, and random advice of less than 5 percentage points on the choice proportion. The sample size was also chosen to support analyses of heterogeneity across choice problems and participants. In particular, the study examines the correlation of treatment effects at the choice and subject levels, as well as whether characteristics of a choice problem or a participant predict the magnitude of the treatment effect. Such analyses require precise estimation of treatment effects.