Celebrity endorsement in promoting pro-environmental behavior

Last registered on June 16, 2020


Trial Information

General Information

Celebrity endorsement in promoting pro-environmental behavior
Initial registration date
October 23, 2019

Initial registration date is when the trial was registered.

It corresponds to when the registration was submitted to the Registry to be reviewed for publication.

First published
October 23, 2019, 4:08 PM EDT

First published corresponds to when the trial was first made public on the Registry after being reviewed.

Last updated
June 16, 2020, 3:38 AM EDT

Last updated is the most recent time when changes to the trial's registration were published.


Primary Investigator

School of Economics, University of Economics Ho Chi Minh City

Other Primary Investigator(s)

PI Affiliation
Department of Economics, University of Gothenburg, Sweden
PI Affiliation
Economics and Environment for Development Research Program, CATIE, Costa Rica
PI Affiliation
Department of Social Sciences, Wageningen University and Research, The Netherlands
PI Affiliation
School of Economics, University of Economics Ho Chi Minh City, Vietnam
PI Affiliation
Department of Economics, University of Gothenburg, Sweden

Additional Trial Information

Start date
End date
Secondary IDs
There is greatly growing attention to tackle plastic pollution issues. Previous studies proposed various instruments dealing with the plastic problems. Education and information programs are frequently used and examined as a mean promoting pro-environmental behavior. Several different forms of pro-environmental campaigns have been observed, i.e., public engagement activities with the participation of celebrities. However, very little research evaluating those activities or investigating different channels of delivering information to the public, hence enhancing behavior change. These are expected to demonstrate through the current study using field experiments to examine the change in knowledge, attitudes and behavior towards plastic consumption. A sample of 1,560 students living in two largest dormitory systems in Ho Chi Minh City and the Mekong River Delta of Vietnam is collected. There are a control group and three add-on treatment groups including environmental education, celebrity endorsement and personal pledge. Two video clips are designed to serve as the environmental education and celebrity treatments. The personal pledge takes a form of a commitment card delivered to the participant asked to join the celebrity in reducing plastic consumption. The treatment is delivered in a workshop form of about 25 participants each. Each participant will receive a voucher framed as compensation for participation in each stage of the study. The participant will redeem the voucher at an experimental shop. It is designed as an instrument to measure student’s behavior before and after the treatment. In addition, we expect to examine the spill-over effect on other domains, i.e., behavior changes made by the participants’ roommates, using a follow-up survey. Specially, a variation of a dictator game is employed to measure individual’s willingness to contribute to an environmental fund that helps triggering pro-environmental behavior. Various econometric models to examine the treatment effect are expected to provide direct and indirect effect of the treatment as well as relative effect among the different channels. This reveals evidence to inform policy options for behavior changes towards plastic pollution mitigation.

External Link(s)

Registration Citation

Ho, Thong et al. 2020. "Celebrity endorsement in promoting pro-environmental behavior." AEA RCT Registry. June 16. https://doi.org/10.1257/rct.4859-1.2000000000000002
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Experimental Details


There are three primary add-on interventions and a market tool that are being introduced through out this study. The primary interventions included environmental education (EE), celebrity endorsement (CE), and individual pledge by providing a commitment card for the treated participant with the celebrity's signature showing her commitment. The market tool intervention is to introduce a tax policy imposing on the use of single-use plastic items.
Intervention Start Date
Intervention End Date

Primary Outcomes

Primary Outcomes (end points)
Outcomes of interest and measures of outcomes
We are interested in the changes of knowledge, attitude and practices (KAP) of students regarding plastics pollution and general environmental issues. These are the direct outcomes of our intervention on plastic pollution, and the changes of KAPs regarding general/other environmental issues as the indirect outcomes. Knowledge on marine plastic pollution (MPP) issues are measured by student surveys. EE is expected to increase knowledge. Change in knowledge is a validity test of our EE intervention. Attitudes toward MPP issues are also measured by student surveys. EE is expected to lead to more positive attitudes toward environmental issues. Practices that help mitigate MPP issues are measured through both self-reported behavior in surveys and behavior observed in the field using field experiments. Changes in behavior is the key outcome because our intervention is aimed to influence.
Primary Outcomes (explanation)

Secondary Outcomes

Secondary Outcomes (end points)
Secondary Outcomes (explanation)

Experimental Design

Experimental Design
We introduce an shop experiment to observe the consumption behavior of the participant toward plastic issues. Each participant will be offered a gift voucher of 110,000 VND to trade a fixed set of good items. This includes some packed milk, yogurt boxes, instant noodle packages, some candies, pens and a soft drink. These are among the most commonly consumed by students and the bundle of goods may require some single-plastic items, i.e., bags, straws and spoons.
Experimental Design Details
Choosing celebrity
The candidate celebrity in this study is Hoang Thuy, who is best known for winning cycle 2 of Vietnam's Next Top Model. She is the first runner-up at the Miss Vietnam Universe 2017 pageant. She will represent Vietnam at the Miss Universe 2019 pageant. Our first pre-test with around 245 Vietnamese university students in April 2019 showed that over 65% of respondents know her. In addition, the pretest results also indicated that using celebrity endorsement in promoting pro-environmental behaviors is crucial (see appendix 2). We conducted a second round pre-test with a special focus on students’ perceptions of Hoang Thuy’s suitability as an endorser for plastic pollution campaigns. The results support our choices of celebrity endorser for this study. Over 80% respondents heard about Hoang Thuy (heard_of_HT) and 44% were aware of her engagement in environmental protection movement (HT_cleanup). Sixty percent respondents expressed positive view of her being able to inspire young people, while only 4% holds negative views (HT_inspire). Finally, 71% of respondents were positive about her being a suitable endorser for combating plastic pollution and only one respondent held a negative view on this (HT_plastic). Furthermore, respondents consider celebrity’s knowledge and experience as the most important aspect when judging the suitability of celebrity endorsers. Miss Hoang Thuy’s personal engagement in the effort to reduce plastic pollution fits this criterion perfectly. Based on the two round of pre-tests, we believe that Miss Hoang Thuy is an appropriate choice of celebrity endorser for this study.

We expect to capture the behavior changes as major outcome variables in natural field settings in several ways. First, we observe participants’ consumption of single-use plastic in a natural shop setting. We pay all participants , from both control and treatment groups, in our study with vouchers and they exchange the vouchers with a set of goods at the designated shops in the campus/students village. The set of the goods are things that commonly consumed by students, including a pack of milk, a soda drink, a pen and a container of mint tablet candy. These items are selected after consulting with a group of students. We work with the shops so that the students can exchange this set of goods at their cashier counter. They can decide whether to take plastic straws and use plastic bags at the counter when they finish the exchange. We do not add anything in the exchange process that may remind the students of the content of our study.
This setting provides a natural shopping environment for the students, so we can observe unprompted decisions of the students. We have an assistant at each counter to check the student ids, deliver the goods and record the plastic use for each student. We train the assistants to record the plastics use by marking the received vouchers with obscure symbols so that the students will not notice we are recording their plastic consumption. This setting will be repeated after baseline survey, after the workshops and after the endline survey. The vouchers are framed as compensation for participation in each stage of the study. The vouchers are only valid for five days and they are not transferable. Shops are chosen among the shop systems right at the or in close vicinity of the dormitory buildings to facilitate the exchanges. We expected that majority of the sampled students will come to the shop to exchange the voucher right after the voucher is handled. The key outcome variable is how many single use plastic items (i.e. straws and bags) a student use in each exchange. As well, we can also measure the time difference between the time point when the voucher is handled, and the time point when it is redeemed.
Second, we observe students’ voluntary participation in marine litter clean-up operations. We organize a trash clean-up event with the direct the help of the EfD Vietnam policy outreach and communication team sometime after the endline survey. We contact all the participants and invite them to join in the clean event in the vicinity (beach, lake or river side, a park). We use their signing-up decisions as a measure of real-life willingness to mitigate MPP problem.
Changes in KAPs regarding general environmental issues and PEB are the outcomes for potential spillover effects to PEB in other domains. Similar to measuring KAPs regarding plastic pollution, we measure awareness, knowledge and attitudes regarding other environmental issues with self-reported surveys questions. Beside the survey questions, we also measure pro-environmental behavior with an experiment. Specifically, we use a variation of a dictator game to measure individual’s willingness to contribute to an environmental NGO that does not focus on plastic pollutions. Every participant who finishes all stages of this study is entitled to a certain amount of money (i.e., 110 thousand VND ), as a bonus payment for the completing our study. Before delivering the money, we offer students an option to donate money out of the bonus payment to an environmental NGO. They can choose to donate any amount between 0 to 110 thousand VND and keep the rest to themselves. We will transfer the donations to the environmental NGO under the names of the individual students. We use the amounts donated to the NGO as a measure of the spillover effects on pro-environmental behavioral beyond the plastics pollution.
The randomly selected roommates of the workshop participants are also invited to the follow-up online survey. The purpose of this survey is to investigate the spillover effect to the participants’ peers, i.e., the spread of knowledge. We offer some lucky gifts that randomly drawing about 5% of the follow-up survey participants may receive a lucky gift and record their post-intervention consumption choices.

Randomization Method
In order to reduce contamination of treatment and study potential spillover effects of the treatment, our treatment assignment is randomized at dormitory room level. We use all the undergraduate dormitory rooms as our sampling frame. We randomly select rooms for the study and randomly assign selected rooms to the treatment or control groups. We randomly select one student in each room as participants of the workshops, as our research subjects for the study of direct effects and randomly one of their roommates in each room for the study of spillover effects. Given we only pick one student in each room, within our sample, randomization occurs at individual level.
Randomization Unit
First sampled number of rooms are randomly selected. Then, in each room there is a student is randomly invited to participate in this study.
Was the treatment clustered?

Experiment Characteristics

Sample size: planned number of clusters
About 1,560 rooms
Sample size: planned number of observations
1,560 students
Sample size (or number of clusters) by treatment arms
390 students control, 390 students environmental education (EE), 390 students EE and celebrity endorsement (CE), 390 students EE, CE and individual pledge.
Minimum detectable effect size for main outcomes (accounting for sample design and clustering)
Given that we have a relatively large sample in each treatment arm and we randomize the treatment allocation at individual level, , our experiment is able to detect relatively small effect size. Note that despite we collect panel data for the estimating the direct effect on the workshop participants, we can only test some other hypotheses with post-intervention cross-sectional data. Therefore, we calculate the minimum detectable effect sizes conservatively assuming we only have post-intervention cross-sectional data. For a binary outcome variable, such as use single-use plastics or not, assuming that 90% of the participants in the control group takes use single-use plastics and there and the attrition rate is 10%, we can detect a reduction by 8 percentage points using a two-sided chi-squared test with a statistical power of 0.8 at the significant level of 0.05. For a continuous outcome variable like the amount fo donation to an environmental NGO, we can detect an effect that equals to 21% of the standard deviation of the donations in the control group using a two-sided t-test with a power of 0.8 at the significant level of 0.05. The minimum detectable effect size is much smaller that the effects found in studies that examines the effects of educational video on pro-environmental behavioral (e.g. Giglio et al. 2018).
Supporting Documents and Materials

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Institutional Review Boards (IRBs)

IRB Name
University of Economics Ho Chi Minh City, Vietnam
IRB Approval Date
IRB Approval Number
Analysis Plan

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Post Trial Information

Study Withdrawal

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Is the intervention completed?
Data Collection Complete
Data Publication

Data Publication

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Program Files

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Reports, Papers & Other Materials

Relevant Paper(s)

Reports & Other Materials