Experimental Design Details
We designed a randomized field experiment to evaluate the effectiveness of monetary incentives to promote recycling. We are exploiting real-time microdata on bio-waste disposal to evaluate the intervention. The field-work is executed by a team of environmental educators who are interacting directly with citizens in a Spanish densely populated city (Palma). The educators will be present at different informational points in the area of the study. The educators provide information on the recycling program, provide households with a free recycling kit, and invite citizens to participate in the study. On specific days with a high expected influx of people, members of the research team might assist environmental educators to administer the treatment.
Participating households will be randomly assigned to a control group (no monetary incentives) and a treatment group (monetary incentives). Households are assigned to one of these two groups by order of recruitment in a staggered way. That is, if the first household is assigned to the treatment group, then the second one is assigned to the control group, and so on.
The municipal company has installed bio-waste containers in different neighborhoods of Palma and now it is installing new containers in additional neighborhoods. As a consequence, we implement two different recruitment periods to study the proposed intervention. The first one corresponds to the period November 2020-March 2021 and the second one corresponds to the period April 2021-November 2021.
The two treatments of the intervention are characterized as follows:
(a) Control group (no incentives): By participating in the study, they can win a prize in cash. A total of 10 prizes of € 280 each will be raffled among those who have agreed to participate in the study (5 prizes corresponding to the first recruitment period and 5 prizes corresponding to the second one). The prize draw is completely independent of the use of the bio-waste container.
First recruitment period: The draw will take place in May 2021.
Second recruitment period: The draw will take place in January 2022
(b) Treatment group (incentives): By participating in the study, they can win a prize in cash. A total of 10 prizes of € 280 will be raffled among the participants (5 prizes corresponding to the first recruitment period and 5 prizes corresponding to the second one).
- The prizes for the first recruitment period will be drawn based on the information registered in the system of electronic bins from the moment of the intervention until 15/04/2021. Each week that any card from the household is registered in the bio-waste container system, the household will acquire a ticket for the raffle. The more tickets the household obtains, the higher chance of winning one of the prizes. The draw will take place in May 2021.
- The prizes for the second recruitment period will be drawn based on the information registered in the system of electronic bins from the moment of the intervention until 15/12/2021. Each week that any card from the household is registered in the bio-waste container system, the household will acquire a ticket for the raffle. The more tickets the household obtains, the higher chance of winning one of the prizes. The draw will take place in January 2022.
A reminder will be sent to the two experimental groups at the time when the removal of the incentives approaches (between 1 and 7 days in advance).
Timing of the intervention:
First recruitment period:
Recruitment of participating households will take place from November 2nd, 2020 to March 31st, 2021.
Incentives in the treatment group will be present from the recruitment week to April 15th, 2021. A reminder will be sent to the two experimental groups at the time when the removal of the incentives approaches (between 1 and 7 days in advance).
Second recruitment period:
Recruitment of participating households will take place from April 6th, 2021 to November 30th, 2021.
Incentives in the treatment group will be present from the recruitment week to December 15th, 2021. A reminder will be sent to the two experimental groups at the time when the removal of the incentives approaches (between 1 and 7 days in advance).
Intervention evaluation period:
First recruitment period:
The direct effect of the intervention will be evaluated using the real-time data from bio-waste bins from the moment of being recruited to April 15th, 2021. Data prior to recruitment time will be used for pre-treatment balancing tests. Data from at least three months posterior to the raffle will be used to analyze the effects after removing the incentives.
Second recruitment period:
The direct effect of the intervention will be evaluated using the real-time data from bio-waste bins from the moment of being recruited to December 15th, 2021. No-pretreatment data will be available for most of the subjects recruited in the second period as the recruitment will take place simultaneously with the installation of electronic bio-waste bins for a majority of the participating households in the second period. Data from at least three months posterior to the raffle will be used to analyze the effects after removing the incentives.
Place of the intervention: Palma (Balearic Islands, Spain) The intervention is conducted only in the areas of the city where the bins for biowaste recycling were introduced. However, the bio-waste recycling program was not simultaneously introduced in all these areas. Implementation was done in different phases. The neighborhoods included in each phase are:
Phase 1 (November 2018): Son Flor, Los Almendros-Son Pacs, Son Rapinya, Son Cotoner, El Fortí & El Camp d'en Serralta
Phase 2 (March 2019): Son Dameto Son & Espanyolet
Phase 3 (November 2020): Santa Catalina, Son Armadans, Son Dureta & La Teulera.
Phase 4 (April 2021) Bons Aires, Camp Redó, Son Peretó, Cas Capiscol, Es Jonquet
Phase 5 (April 2021) Son Anglada, Son Roca, Son Serra-La Vileta, Son Vida, Son Xigala, Son Ximelis
Phase 6 (April 2021) Cala Major, El Terreno, La Bonanova, Porto Pi, Sant Agustí
Phase 7 (May 2021) Amanecer, Arxiduc, L'Olivera, Plaça de Toros, Son Oliva.
Phase 8 (May 2021) Establiments, Secar de la Real, S'Indioteria Urbà.
Phase 9 (May 2021) El Vivero, Estadi Balear, Verge de Lluc, Rafal Nou, Rafal Vell, Son Cladera, Son Fortesa Nord, Son Rullan.
Electronic bio-waste bins were installed substantially earlier in Phase 1 and 2. Moreover, these phases were exploited for conducting a previous trial (soft-commitments and feedback). Consequently, the particularities of households from these areas must be taken into account when evaluating the intervention. Those households that participated in a previous trial (soft-commitments and feedback) will be excluded from analyzing the effect of the present intervention. However, they will not be excluded from the possibility of participating to avoid potential complaints about being excluded from the possibility of winning a prize. In Phases 1, 2, and 3, the administration of the treatment started after the installation of the electronic bio-waste bins, thus pre-intervention data will be available for balancing tests. This is not the case for phase 4 and posterior ones, which implies that pre-intervention data on disposals will often not be available for households in these areas.
When an additional neighborhood is incorporated into the recycling program during the intervention, it will be included both in the intervention and in the primary sample for evaluating the intervention.
During the first two weeks of the intervention, it is considered that the educators are still learning and refining the administration of the protocol. Consequently, data coming from this period (from November 2 to November 16) will be analyzed in detail to determine its validity and assess whether or not the households recruited in this period are included in the final sample. Independently of its inclusion, the final decision will be explained and motivated in the paper.
In the event that educators run out of recycling kits, households would continue to be recruited for their participation to maintain a sufficiently large sample size. These observations will be conveniently treated during the data analysis.