| Field | Before | After |
|---|---|---|
| Field Trial End Date | Before May 05, 2026 | After July 10, 2026 |
| Field Last Published | Before April 21, 2026 03:00 PM | After July 02, 2026 06:51 AM |
| Field Intervention (Public) | Before Participants take part in an online decision task in which they choose how many units of a product to purchase at a fixed price that reflects a carbon-related charge. Purchasing fewer units is associated with greater environmental benefits. Depending on the treatment group, participants may receive no cash rebate, a guaranteed cash rebate, or a cash rebate that is awarded with a specified probability. The size of the rebate is fixed, but the likelihood of receiving it varies across groups. Participants make decisions in four rounds and receive feedback about outcomes after each decision round, with one round randomly selected to determine their final payoff. In a later amendment to the original five-arm design, we added a sixth treatment arm, the Neutral Pricing Benchmark, in which participants complete an otherwise identical purchase task with the same prices, values, feasible choice set, number of rounds, and payoff structure, but with no mention of carbon emissions, emissions retirement, or rebates. | After Participants take part in an online decision task in which they choose how many units of a product to purchase at a fixed price that reflects a carbon-related charge. Purchasing fewer units is associated with greater environmental benefits. Depending on the treatment group, participants may receive no cash rebate, a guaranteed cash rebate, or a cash rebate that is awarded with a specified probability. The size of the rebate is fixed, but the likelihood of receiving it varies across groups. Participants make decisions in four rounds and receive feedback about outcomes after each decision round, with one round randomly selected to determine their final payoff. In a later amendment to the original five-arm design, we added a sixth treatment arm, the Neutral Pricing Benchmark, in which participants complete an otherwise identical purchase task with the same prices, values, feasible choice set, number of rounds, and payoff structure, but with no mention of carbon emissions, emissions retirement, or rebates. Amendment: In addition to the original experimental arms, we add a supplemental data-collection wave focused exclusively on the 50% probabilistic rebate and 100% guaranteed rebate treatments. New participants in this wave will be randomized in equal proportions between these two treatments. The decision task, payoff structure, rebate amount, and CO₂-offset mapping are kept the same as in the original study. |
| Field Intervention End Date | Before May 05, 2026 | After July 10, 2026 |
| Field Primary Outcomes (End Points) | Before The primary outcome is the number of units purchased in Round 1, Yi1 = {0,1,2,3,4}, treated as continuous. This measure also provides the participants desired level for the experimenters commitment to retire carbon emission allowances equivalent to 50 pounds of CO2 per unit not purchased. | After The primary outcome is the number of units purchased in Round 1, Yi1 = {0,1,2,3,4}, treated as continuous. This measure also provides the participants desired level for the experimenters commitment to retire carbon emission allowances equivalent to 50 pounds of CO2 per unit not purchased. Supplemental primary outcome: number of units purchased in Round 4 in the 50% and 100% rebate treatments. This round-specific endpoint is used for the supplemental non-inferiority analysis because the original results and reviewer concern focused on whether the 50% rebate remains close to the 100% rebate after participants have gained experience with the repeated decision environment. Secondary supplemental outcomes include units purchased in Rounds 1–3 and the average number of units purchased across rounds. |
| Field Experimental Design (Public) | Before The study uses a between-subjects experimental design with random assignment to one of five incentive conditions: no rebate, sure rebate, or a probabilistic rebate with a 50%, 25%, or 10% probability. Participants complete a sequence of four decision rounds. In each round, they choose how many units (0–4) of a fictitious consumption good to purchase at a fixed price. Each unit provides a privately induced monetary value to the participant, while consumption is associated with carbon emissions that can be offset by the researchers depending on participants' choices. In rebate conditions, participants are informed that they may receive a monetary rebate linked to the number of units they choose not to consume. The structure of the rebate varies by treatment in terms of the probability with which it is paid. Participants receive feedback after each round about their own choices and the corresponding carbon offset. At the end of the experiment, one round is randomly selected to determine monetary payoffs. Randomization is conducted at the individual level, and all participants face the same price, values, and decision environment aside from the rebate probability. The design allows comparison of choices across incentive conditions and across rounds within individuals. In a later amendment, a sixth condition was added: the Neutral Pricing Benchmark. | After The study uses a between-subjects experimental design with random assignment to one of five incentive conditions: no rebate, sure rebate, or a probabilistic rebate with a 50%, 25%, or 10% probability. Participants complete a sequence of four decision rounds. In each round, they choose how many units (0–4) of a fictitious consumption good to purchase at a fixed price. Each unit provides a privately induced monetary value to the participant, while consumption is associated with carbon emissions that can be offset by the researchers depending on participants' choices. In rebate conditions, participants are informed that they may receive a monetary rebate linked to the number of units they choose not to consume. The structure of the rebate varies by treatment in terms of the probability with which it is paid. Participants receive feedback after each round about their own choices and the corresponding carbon offset. At the end of the experiment, one round is randomly selected to determine monetary payoffs. Randomization is conducted at the individual level, and all participants face the same price, values, and decision environment aside from the rebate probability. The design allows comparison of choices across incentive conditions and across rounds within individuals. In a later amendment, a sixth condition was added: the Neutral Pricing Benchmark. Amendment: During peer review, a referee raised the concern that the absence of a statistically significant difference between the 50% and 100% rebate treatments should not be interpreted as equivalence, and that the existing comparison was underpowered to rule out small but meaningful differences. In response, we add a supplemental confirmatory non-inferiority analysis comparing the 50% probabilistic rebate to the 100% guaranteed rebate. This supplemental analysis does not replace the originally preregistered primary comparison between the 100% and 10% rebate treatments. |
| Field Randomization Method | Before Randomization is implemented by the experimental software (Qualtrics or oTree). Participants are randomly assigned to one of the treatment conditions upon entering the study by the experimental software. | After Randomization is implemented by the experimental software (Qualtrics or oTree). Participants are randomly assigned to one of the treatment conditions upon entering the study by the experimental software. For the supplemental wave, eligible participants will be randomized in equal proportions between the 50% probabilistic rebate and 100% guaranteed rebate treatments. |
| Field Sample size (or number of clusters) by treatment arms | Before Neutral Pricing Benchmark (added in amendment): 104 participants No rebate (control): 104 participants Sure rebate (100%): 362 participants 50% rebate: 104 participants 25% rebate: 104 participants 10% rebate: 362 participants Total: 1,140 participants | After Neutral Pricing Benchmark (added in amendment): 104 participants No rebate (control): 104 participants Sure rebate (100%): 362 participants 50% rebate: 104 participants 25% rebate: 104 participants 10% rebate: 362 participants Total: 1,140 participants The supplemental wave targets 521 completed observations in the 50% rebate treatment and 521 completed observations in the 100% rebate treatment, for 1,042 new completed observations. Combined with the original completed observations, (n50_old=114) and (n100_old=378), the final pooled comparison will include 635 observations in the 50% rebate treatment and 899 observations in the 100% rebate treatment, for a total of 1,534 observations in the 50% versus 100% comparison. |
| Field Intervention (Hidden) | Before Participants complete an online, incentivized experiment in which they make four repeated consumption decisions under a fixed price that incorporates a carbon-related charge. In each round, participants choose an integer number of units n={0, 1, 2, 3, 4} of a fictitious product. Each unit provides a declining private value: the first unit yields a value of $15, the second unit a value of $14.5, the third unit a value of $14 and the fourth unit a value of $13.5. The price per unit is fixed at $13 in all rounds and treatments. Monetary payoffs in each round are determined by the sum of the private values of the units purchased minus total expenditures. Consumption choices are linked to real environmental consequences. For each unit not consumed, the experimenters commit to retire carbon emission allowances equivalent to 50 pounds of CO2. Thus, if a participant foregoes all four units, 200 pounds of CO2 are retired; if three units are foregone, 150 pounds of CO2 are retired; if two units are foregone, 100 pounds are retired; if one unit is foregone, 50 pounds are retired; and if all four units are purchased, no allowances are retired. These offsets are implemented by the research team upon completion of the study. Participants are randomly assigned to one of several treatment conditions that differ in the presence and structure of a cash rebate. In the no-rebate control condition, participants receive no rebate regardless of their consumption choices. In the sure rebate condition, participants receive a guaranteed rebate of $2 for each unit not consumed. In probabilistic rebate conditions, the per-unit rebate amount remains $2, but it is awarded only with a specified probability. Specifically, participants in the 50% treatment receive the rebate with 50% probability, participants in the 25% treatment receive it with 25% probability, and participants in the 10% treatment receive it with 10% probability. In probabilistic treatments, the rebate lottery is resolved independently at the end of the experiment for the payoff-relevant round. The decision task is repeated for four rounds. To preserve incentive compatibility while limiting total payments, one of the four rounds is randomly selected at the end of the experiment to determine the participant's final payoff. Participants receive feedback after each round about their monetary payoff and the associated carbon offset. All payments are made in real money. In addition to the main decision task, participants complete a short incentivized task to elicit individual risk preferences, as well as a demographic questionnaire. The experimental design allows for a comparison of consumption behavior under guaranteed versus probabilistic rebate schemes and for an assessment of how responses vary systematically with the probability of receiving a rebate, while holding prices and private values constant. In a later amendment to the preregistered design, we added a sixth treatment arm: the Neutral Pricing Benchmark. In this treatment, participants complete an otherwise identical decision task with the same prices, values, feasible choice set, number of rounds, and payoff rule, but there is no mention of carbon emissions, emissions retirement, or rebates. Participants are simply told the unit price and the monetary consequences of their choices. This arm was added to provide a benchmark for whether participants choose the privately optimal quantity when environmental content and rebate-related considerations are removed. | After Participants complete an online, incentivized experiment in which they make four repeated consumption decisions under a fixed price that incorporates a carbon-related charge. In each round, participants choose an integer number of units n={0, 1, 2, 3, 4} of a fictitious product. Each unit provides a declining private value: the first unit yields a value of $15, the second unit a value of $14.5, the third unit a value of $14 and the fourth unit a value of $13.5. The price per unit is fixed at $13 in all rounds and treatments. Monetary payoffs in each round are determined by the sum of the private values of the units purchased minus total expenditures. Consumption choices are linked to real environmental consequences. For each unit not consumed, the experimenters commit to retire carbon emission allowances equivalent to 50 pounds of CO2. Thus, if a participant foregoes all four units, 200 pounds of CO2 are retired; if three units are foregone, 150 pounds of CO2 are retired; if two units are foregone, 100 pounds are retired; if one unit is foregone, 50 pounds are retired; and if all four units are purchased, no allowances are retired. These offsets are implemented by the research team upon completion of the study. Participants are randomly assigned to one of several treatment conditions that differ in the presence and structure of a cash rebate. In the no-rebate control condition, participants receive no rebate regardless of their consumption choices. In the sure rebate condition, participants receive a guaranteed rebate of $2 for each unit not consumed. In probabilistic rebate conditions, the per-unit rebate amount remains $2, but it is awarded only with a specified probability. Specifically, participants in the 50% treatment receive the rebate with 50% probability, participants in the 25% treatment receive it with 25% probability, and participants in the 10% treatment receive it with 10% probability. In probabilistic treatments, the rebate lottery is resolved independently at the end of the experiment for the payoff-relevant round. The decision task is repeated for four rounds. To preserve incentive compatibility while limiting total payments, one of the four rounds is randomly selected at the end of the experiment to determine the participant's final payoff. Participants receive feedback after each round about their monetary payoff and the associated carbon offset. All payments are made in real money. In addition to the main decision task, participants complete a short incentivized task to elicit individual risk preferences, as well as a demographic questionnaire. The experimental design allows for a comparison of consumption behavior under guaranteed versus probabilistic rebate schemes and for an assessment of how responses vary systematically with the probability of receiving a rebate, while holding prices and private values constant. In a later amendment to the preregistered design, we added a sixth treatment arm: the Neutral Pricing Benchmark. In this treatment, participants complete an otherwise identical decision task with the same prices, values, feasible choice set, number of rounds, and payoff rule, but there is no mention of carbon emissions, emissions retirement, or rebates. Participants are simply told the unit price and the monetary consequences of their choices. This arm was added to provide a benchmark for whether participants choose the privately optimal quantity when environmental content and rebate-related considerations are removed. Amendment: In addition to the original experimental arms, we add a supplemental data-collection wave focused exclusively on the 50% probabilistic rebate and 100% guaranteed rebate treatments. New participants in this wave will be randomized in equal proportions between these two treatments. The decision task, payoff structure, rebate amount, and CO₂-offset mapping are kept the same as in the original study. |
| Field | Before | After |
|---|---|---|
| Field Document | Before | After |
| Field | Value |
|---|---|
| Field Document |
Value
carbon_pricing_and_lottery_incentives.pdf
MD5:
ff2fc633ff25d0c5c8811e660947c28e
SHA1:
a30338ba965eba2f31e7e276ea3b46d0fa5e8b71
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