Vouchers to increase the affordability of fruits and vegetables in Nigeria and Vietnam

Last registered on August 16, 2022


Trial Information

General Information

Vouchers to increase the affordability of fruits and vegetables in Nigeria and Vietnam
Initial registration date
August 06, 2021

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
August 09, 2021, 5:17 PM EDT

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

Last updated
August 16, 2022, 10:20 AM EDT

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



Primary Investigator

International Food Policy Research Institute

Other Primary Investigator(s)

PI Affiliation
PI Affiliation

Additional Trial Information

Start date
End date
Secondary IDs
Prior work
This trial does not extend or rely on any prior RCTs.
Low consumption of fruits and vegetables is a rising global health concern in both low and high-income economies. As countries become increasingly urbanized, ultra-processed foods high in fat, salt, and sugar become increasingly popular, contributing to the triple burden of malnutrition. Given that affordability is a major determinant of households' food consumption choices, we will estimate the effect of increasing affordability of fruits and vegetables in Nigeria and Vietnam by providing households with weekly coupons for discounts on the prices of certain fruits and vegetables at their local markets. The intervention will be implemented as a randomized control trial (RCT), with two treatment groups and a control group, to allow for causal estimates of the impact of these coupons. Households in treatment group one will receive coupons that are half as large as the coupons given to treatment group two to test the difference between an inframarginal coupon (one that is below their existing consumption level), and an extramarginal coupon (one that is above their existing consumption level).
External Link(s)

Registration Citation

Ambler, Kate, Alan de Brauw and Sylvan Herskowitz. 2022. "Vouchers to increase the affordability of fruits and vegetables in Nigeria and Vietnam." AEA RCT Registry. August 16. https://doi.org/10.1257/rct.7701-1.1
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Experimental Details


This project will implement a coupon intervention that is designed to increase the affordability of fruits and vegetables.
• Coupons will be printed on paper and distributed directly to households. We investigated the possibility of using digital coupons, but exploratory work in both countries suggests that paper coupons will be more effective and easier to use for participants. Coupons will be personalized with the household name and a code to prevent sharing of coupons.
o Printing the household name on the coupon will emphasize the intentions of the program and raise accountability of transfers away from the beneficiary family. We will additionally develop a further verification system at point of redemption that is appropriate for each context. In order to reduce the possibility of counterfeit coupons, all coupons will also be stamped with a specially designed project stamp that would be very difficult to counterfeit.
o We plan to deploy a number of “fake shoppers” employed by the project to the vendors as a mode of auditing the vendors in initial stages of the project. These will be people from the selected communities who appear like other participants and who will be given coupons to redeem for produce as if they are, in fact, study participants. This will allow us to ensure that vendors are following the study’s protocols. Vendors will be aware that this auditing will occur, this knowledge is a key component of the motivation of vendors to properly follow project procedures.
• Coupons will target certain types of fruits and vegetables and each coupon can be used to buy just one product or a mix depending on what the vendor has available. These will be chosen based on analysis of the 24 hour recall data, identifying nutritional gaps in household consumption for the sample while accounting for seasonal availability of different goods. Preliminary analysis shows that fruits in general are highly under-consumed in both countries, so it is strongly likely that the coupons will be focused on different types of fruit. The household survey data reveals that households are already eating fruits and vegetables, so focusing on under-consumed varieties and frequencies is important. To target these fruits and vegetables, the coupons will have pictures of the permitted produce printed on the paper coupon. Because appropriate fruits and vegetables may vary across seasons, we will include options from different seasons on the coupons so that the coupons do not need to be changed mid-project. Vendors will be instructed not to accept coupons for fruits and vegetables not pictured on the coupons, and this will be monitored through our project auditing (fake shoppers).
• While we considered percentage discounts, given the large number of vendors, their limited capacity, and their informal nature, we determined that discounts would be unenforceable and difficult to implement. Instead, we determined that vouchers for specific amounts (i.e. $1 of fruits and vegetables) are the most practical alternative.
• Coupons will be distributed weekly for six months. Each coupon will be valid for one to two weeks.
• Coupons will be redeemable with vendors within markets. A major challenge of this project is that we have learned that the participants purchase their produce in a large variety of markets, formal and informal, and from informal sellers in the neighborhood. A primary goal of the project is to not force people to change their purchasing behavior unless they decide to do so for themselves. While working with every fruit or vegetable vendor in these communities would not be logistically feasible, we will be as inclusive as possible. To this end, we will include as many vendors as possible in each of the major market areas in each community to avoid imposing significant additional shoe-leather costs that could impede usage of the coupons. Focus groups suggested that this approach would be acceptable to consumers and that requiring redemption with a vendor in one of the major market locations in their community would not be a major deterrent to their usage of the coupons. A possible issue in Nigeria is that children may be selling vegetables, and we do not want to encourage child labor, as such we will be cognizant of this in piloting and in the selection of vendors to participate in the project. Consumers will receive education on how to redeem coupons when recruited into the project.
• To facilitate enrolling enough vendors, we will employ agents who can accept the coupons from vendors and reimburse them for the cost. Agents may be recruited by the project, or existing agents of financial institutions already working in the markets. If working through existing structures, covering large numbers of markets and vendors would be simple. If recruiting project agents, they could visit a number of locations every day (or every couple of days) to ensure efficiency.
• Participating vendors will receive a small incentive payment for each coupon that is successfully redeemed.
Project design will also be cognizant of ethical considerations in particular in considering possible negative spillovers to non-participating vendors and consumers. In general, the number of participants in our study relative to the overall size of the neighborhoods and markets is small, as such the coupons should not have any general equilibrium effects on prices. There is a risk that a non-participating vendor could lose a customer who has a coupon to a participating vendor. Overall, given the large number of vendors in these markets, and our commitment to enrolling as many vendors as practical, we expect these negative spillovers to be marginal. However, attention will be paid to this issue during piloting to ensure to the greatest extent possible that all risks are minimized.
Intervention Start Date
Intervention End Date

Primary Outcomes

Primary Outcomes (end points)
Days consumed (fruits and vegetables) in last 7 days
Types consumed in the last 7 days
Expenditures on target items in the last 7 days
Primary Outcomes (explanation)

Secondary Outcomes

Secondary Outcomes (end points)
Fruits: Days consumed in the last 7 days, types consumed in the last 7 days, and expenditures on fruits in the last 7 days
Vegetables: types consumed in the last 7 days, and expenditures on vegetables in the last 7 days
Expenditures on other food in the last 7 days
Individual dietary diversity (of interviewed woman) using the GALLUP tool
Children's dietary diversity
Secondary Outcomes (explanation)
We do not include days vegetables consumed because the baseline average is already close to 7.

Experimental Design

Experimental Design
The goal of this study is to understand the impact of providing coupons for fruit and vegetable on the consumption behavior of the household, both at the individual level and overall. To do this we will conduct a randomized evaluation of the coupon program. Participants will be randomized, at the individual level, into three groups:
1. Control: Participants in the control group will not receive any intervention.
2. Small coupons: Participants in this treatment group will receive weekly coupons in a “small” amount. This amount will be determined to be below the average weekly consumption at baseline for the designated fruits and vegetables.
3. Large coupons: Participants in this treatment group will receive weekly coupons in a “large” amount. This amount will be determined to be above the average weekly consumption at baseline for the designated fruits and vegetables.
The small and large coupon sizes are designed to test the difference between an inframarginal coupon (one that is below their existing consumption level), and an extramarginal coupon (one that is above their existing consumption level). A voucher for an amount below what is normally spent means that an individual could use that voucher and purchase their normal amount of that item, and use the savings on other things. If they increase their consumption, it is because they were previously consuming less than they desired due to their budget constraint. If however they do not increase their consumption that indicates they are already consumed their preferred amount. In that case, the large extramarginal coupon would be needed to incentivize increased consumption. As that coupon is larger than their current consumption levels, they would need to increase consumption in order to not waste the voucher.
We are concerned that the non-divisibility of the coupons will limit their usefulness, people may shop for different fruits at different stands, or make multiple trips per week given that these are perishable items. As such we will pilot offering three smaller coupons or one larger coupon, and determine which we should include in the project implementation.
We seek to answer the following research questions:
• Does providing coupons (vouchers) for fruits and/or vegetables increase the consumption of the specific products on the voucher? Of fruits and/or vegetables in general?
• Does providing coupons crowd in additional expenditures on fruits and vegetables?
• Does providing coupons affect other consumption patterns?
• How much does the size of the voucher matter?

We will examine these questions both during the intervention itself, and 2-3 months following the conclusion of the intervention to assess whether the intervention has lasting impacts on the following outcomes.
We hypothesize that by providing coupons for specific fruits and vegetables, households will purchase and consume more of those specific fruits and vegetables. Consumption of targeted items will be our primary outcome. We further hypothesize that the coupons will further increase consumption of fruits and vegetables generally; in other words, substitution would occur only from other types of food, or any substitution that would occur away from other fruits and vegetables would be dominated by the positive effect on demand of the coupons.

To address multiple hypothesis testing we will create an index for each of the three consumption categories (targeted outcomes, fruits, and vegetables), and also calculate sharpened q-values within each family (Anderson 2008). We will additionally calculate sharpened q-values across the dietary diversity outcomes.
We will also examine several exploratory outcomes. These are intended to track understanding of how the vouchers affected other types of behavior related to consumption. Because these are exploratory we will not apply any multiple hypothesis testing.

Randomization into the treatment groups will be conducted at the household level in each country. Randomization will be stratified by the neighborhood and the median level of baseline fruit consumption (ie households will be split into two groups based on sample median baseline fruit consumption). We will randomize the households into the control group, the small voucher group, and the large voucher group, with equal numbers of households per treatment arm. That randomization will be stratified on neighborhood and median level of baseline fruit consumption.
Potential competing studies are the other intervention elements of the overall project. These will be implemented in the same neighborhoods are our study. We will rely on the randomization to ensure that we are able to calculate an unbiased estimate of the impact of the coupons. If possible, we will control for exposure to the other interventions.

Data collection
The evaluation will be conducted using several sources of data. Baseline data will come from the household survey which has already been completed. Evaluation of the program’s impact will use three sources of follow-up data.

Monitoring surveys
The project plans to conduct short monitoring surveys with a rotating cross section of the baseline sample. While details are still being finalized, current plans are to interview approximately 50 households per month for 12 months. The 12 month period will coincide with the 12 month implementation period of WP2a and WP2c. Ideally the 6 month implementation of the coupon intervention will be timed so that the monitoring data covers a couple of months prior to the intervention beginning, the period of the intervention, and several months after. These monitoring surveys are designed to proxy 24 hour recall data, collecting data on which food types were consumed in the previous 24 hours, without a full accounting of all values and quantities. It will also contain some limited data regarding consumption in the previous 7 days. Given small sample sizes, we anticipate using this as a complementary (but not primary) data source for our evaluation.

Endline survey 1
The first endline survey, designed as a monitoring survey for WP2b, will take place in the final month of the coupon intervention implementation, while households are still receiving coupons. It will allow us to measure the impacts of the intervention during implementation.

Endline survey 2
The second endline survey, is the project endline survey. Implementation of the coupon intervention will be designed so that this survey is conducted 2 to 3 months after the conclusion of the intervention, and will allow us to measure the persistence of impacts.
Experimental Design Details
Randomization Method
Randomization done in STATA
Randomization Unit
household level
Was the treatment clustered?

Experiment Characteristics

Sample size: planned number of clusters
598 households in Vietnam, 632 households in Nigeria
Sample size: planned number of observations
598 households in Vietnam, 557 households in Nigeria
Sample size (or number of clusters) by treatment arms
Vietnam: 199 households control, 198 households small coupon, 201 households large coupon
Nigeria: 184 households control, 187 households small coupon, 186 households large coupon
Minimum detectable effect size for main outcomes (accounting for sample design and clustering)
(Assuming 10 percent attrition) Vietnam: Types of vegetables consumed, SD=1.79, MDE 11 % ; Days fruits consumed, SD=2.36, MDE 14% ; Types of fruits consumed, SD=1.76, MDE 17%; Amount spent on food (Vietnamese dong (currency)), SD=524,503.20, MDE 19%; Amount spent on vegetables (dong), SD =77,520.88, MDE 23%; Amount spent on fruit (dong). SD=154,649.39, MDE 27% Nigeria: Types of vegetables consumed, SD=1.74, MDE 9 % ; Days fruits consumed, SD=2.15, MDE 19% ; Types of fruits consumed, SD=1.55, MDE 21%; Amount spent on food (Nigerian naira (currency)), SD=5,103.07, MDE 18%; Amount spent on vegetables (naira), SD =1,446.18, MDE 29%; Amount spent on fruit (naira). SD=958.20, MDE 35%

Institutional Review Boards (IRBs)

IRB Name
International Food Policy Research Institute IRB
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

Is public data available?

Program Files

Program Files
Reports, Papers & Other Materials

Relevant Paper(s)

Reports & Other Materials