Effects of Incentives vs Normative Feedback on Bio-waste Sorting in the Field

INTRODUCTION: The treatment and randomization unit in the study will be households located in the city of Palma (Spain) where individuals must use a personal card to use the bins meant for bio-waste sorting. Hence, each bin use is recorded and associated with one individual, allowing us to track the participants' use of the bio-waste sorting bins.

RECRUITMENT: Participants were recruited between the 1st of March 2023 and lasted until the 30th of June. Recruitment was carried out face-to-face by directly approaching people in the street, by the internet through advertisements in social media, and by placing flyers in the city. The participants were informed that the study would be about their bio-waste sorting behavior and that they would receive messages by WhatsApp; recruitment was facilitated by offering those who signed up to win one of four prizes of €250 each (only one individual per household could sign up). The certified random draw of the winners was performed by the independent firm "Easypromos" on the 27th of July. Each participant signed an informed consent form and answered a questionnaire that collected basic demographic data (number and ages of people in the participant's household, annual income, contact information, …) as well as data on social norms, personal norms, and relationship with nature (beliefs about average environmental sensitivity in the population, motivations to recycle, ...). Among those who signed up, only the citizens of Palma who have the card required to open the bio-waste sorting bins were included in the final sample.

2023-10-17

2024-06-30

- Effect of Wave 1 messages: proportion of weeks that each household uses the bio-waste sorting bin at least once between October 23rd 2023 and February 11th 2024 (Data of the week in which the households receive the WhatsApp message is not analyzed).
- Effect of Wave 2 messages: proportion of weeks that each participant uses the bio-waste sorting bin at least once between February 19th 2024 and the end date (in June or July 2024).

- Effect of Wave 1 messages: average number of bio-waste sorting bin openings per week, between October 23rd 2023 and February 11th 2024 (Data of the week in which the households receive the WhatsApp message is not analyzed).
- Effect of Wave 2 messages: average number of bio-waste sorting bin openings per week, between February 19th 2024 and the end date (in June or July 2024).

This RCT consists of a field experiment about bio-waste recycling in the city of Palma (Spain). Citizens of Palma must scan a card that identifies them in order to use the bins meant for bio-waste sorting. Such bins are available on streets throughout the city, next to the bins for recycling of glass, plastic, and paper. The city's waste management company will provide the research team with data on the bio-waste sorting behaviors of the 1620 households who signed up to participate in the study between February and July 2023. The goal is to study how the participants' use of the bio-waste sorting bins is affected by feedback. The participants will be allocated to one of three treatments. Each participant will receive a first round of feedback messages between October 17 and 20, and then a second round of messages at some point in February 2024.

Not available

Household level randomized by a computer (randtreat command in Stata, with setseed(15)). Stratified by recruitment source (Form, Twitter, street, other)

The randomization unit is the household.

No

1620 households.

Weekly behavior of the 1620 households.

540 households per treatment arm.

According to data collected in previous studies (see Alonso-Paulí et al., 2023), an average household in the city of Palma uses bio-waste sorting bins with a weekly frequency of 0.29, showing a standard deviation of 0.354. For a power analysis of 80%, given the sample size we intend to have, we guarantee, at least, a minimum detectable effect of 0.0767 in the use frequency (at 95% confidence).