Experimental Design Details
The experimental design is conceived to isolate the effects of policy interventions, implemented to induce pro-environmental behavior, on behavioral spillovers effects. To achieve this, we apply five treatments using a between subject design in an artefactual field experiment. These treatments are listed in Table 1 along with information on the incentive schemes applied, the existence of an environmental context in task 1 and the planned number of observations (relies on power analysis, see Figure 1 in Appendix).
Treatment Incentive scheme Environmental context of task 1 Observations
Baseline No incentive X 100
NoIncentive No incentive ✓ 100
Nudge Environmental impact & social information ✓ 100
Money 0. 5€ / answered question ✓ 100
Force Time punishment for not answering correctly ✓ 100
The experimental design is built around a discrete choice experiment and exploits that participants are asked comprehension questions in order to access the decision stage after having read information on the product of relevance. We construct a real effort task by generating a donation to an afforestation project for each correctly answered comprehension question, in which effort materialized in environmental benefit. This represents the first pro-environmental behavior in the experiment. To further incentivize this pro-environmental behavior task, we introduce a nudge, monetary incentives and a punishment mechanism in different treatments. The second pro-environmental behavior task is given by offering subjects the opportunity to donate parts of their payoff to environmental NGOs, which are not related to afforestation or climate. On the last page, a questionnaire must be filled, containing questions on environmental attitudes or demographic information among others. In the following, the treatments are described in more detail.
The ‘baseline’ treatment serves as a control treatment to assess donation behavior in the absence of preceding environmental contributions. In this treatment, subjects are asked to answer the comprehension questions. However, answering correctly has no material consequences, neither for the participants’ payoff, nor in terms of environmental contribution. In the second task, subjects have the option to donate a share of their endowment to three different charities (WWF, NABU, Food Bank Mannheim). The treatment will serve for baseline comparisons, in order to investigate the differences in donations between the baseline treatment and the treatments, in which subjects made an environmental contribution in the first PEB-task. This difference will determine the size of the behavioral spillover effect.
The ‘NoIncentive’ treatment is structured in a similar to the ‘baseline’ treatment. The only difference is given by the consequences of answering the comprehension questions in the first task. Here, each exercise, which is solved by subjects, generates a donation to ‘Eden Reforestation Project’, an environmental NGO that has the objective to engage local citizens in developing countries into afforestation projects. Thereby, solving one exercise generates a donation, which suffices to finance the plantation of a tree in the afforestation project.
The ‘Nudge’ treatment distinguishes from the ‘NoIncentive’ treatment by the means of motivating subjects to perform the first PEB-task. While there is no specific incentivation in the ‘NoIncentive’ treatment, in the ‘Nudge’ treatment subjects receive information on their relative performance compared to other participants in a real time feedback mode. The real time feedback is applied during the process of answering the comprehension questions. Each round it is signaled to participants via emoticons and a graph whether their performance is within the upper 25 percent, average or lower than average performance cluster of participants who have answered this question before. Hence, this treatment aims to increase subjects’ motivation by raising their ambitions to perform better than others and manipulates the social norm by conveying that providing high effort is the socially appropriate behavior.
In the ‘Money’ treatment, solving exercises does not only lead to a contribution to an afforestation project, but also increases subjects payoff by 1€ per question. In order to avoid endowment effects, we assure that each subject is endowed with the same amount of money when taking the donation decision irrelevant of treatment. This is achieved by remunerating subjects in the other treatments for making hypothetical purchase decisions in the discrete choice experiment instead of paying them for each comprehension question.
The ‘Punishment’ treatment is set up similarly to the ‘NoIncentive’ treatment, but is framed to make subjects feel pressured to answer the comprehension questions. In addition, we implement a time punishment for not answering correctly. Subjects who have failed to answer a comprehension question correctly must wait 15 seconds to be able to proceed with the experiment and try to answer the question again.
The NoIncentive treatment is designed in order to determine the behavioral spillover effect in the absence of any incentivation of the first pro-environmental behavior task. The other three treatments (Nudge, Money, Punishment) are conceived to assess if there are significant differences in behavioral spillover effects compared to the ‘NoIncentive’ treatment. We exploit the different degrees of perceived external pressure to perform the task, which are a characteristic of the policy measures applied in the treatments.
The hypotheses comprise of Hypothesis 1, stating that there will be negative behavioral spillover effects, as subjects in the "NoIncentive" treatment will have donated significantly less than subjects in the "baseline" treatment. Also, we assume that the highest external pressure is exerted in the "punishment" treatment, followed by the "Money" treatment and complemented by the "Nudge". The least external pressure is acted upon subjects in the "NoIncentive" treatment. Based on this, it is hypothesized that behavioral spillover effects are crowded out by external pressure of the policy interventions. Therefore, in Hypothesis two, we expect to see the largest donations in "baseline". This is followed by significantly lower donations in the "punishment" treatment and even lower donations in the "money" treatment. The nudge will lower the donatoin level even further and the least donations are expected to be collected in the "NoIncentive" treamtment, based on the external pressure exerted on participants in the treatments respectively.