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When Certification Turns Sour: A Randomized Intervention with Pesticide Testing Agencies in Vietnam

Last registered on January 03, 2020


Trial Information

General Information

When Certification Turns Sour: A Randomized Intervention with Pesticide Testing Agencies in Vietnam
Initial registration date
December 24, 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
January 03, 2020, 5:02 PM EST

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



Primary Investigator

University of Hong Kong

Other Primary Investigator(s)

Additional Trial Information

In development
Start date
End date
Secondary IDs
Information frictions along the supply chain can severely undermine the provision of high quality products and result in a market for lemons. One potential solution to this problem is to attain product certification from external experts. This proposed project investigates why certification may fail to solve the lemons problem driven by asymmetric information on product quality between the producer and the buyer. Through a randomized intervention with dragon fruit farms in Vietnam, I study whether and how producers (i.e. farmers) and buyers (i.e. intermediaries) respond to the testing agency selected for pesticide residue analysis, a critical factor for receiving certification for Vietnam’s Good Agricultural Practices (VietGAP). Specifically, producers are randomly assigned to a testing agency chosen from a list determined by the researcher. I test producer response to the testing agency by comparing pesticide residue levels in dragon fruit across producer groups assigned to different testing agencies. Next, I conduct a survey with buyers to compare their willingness to purchase dragon fruits certified and tested by different agencies.
External Link(s)

Registration Citation

Park, Sangyoon. 2020. "When Certification Turns Sour: A Randomized Intervention with Pesticide Testing Agencies in Vietnam." AEA RCT Registry. January 03.
Experimental Details


This project is a follow-up study to a separate project that evaluates the effects of providing training and certification on Good Agricultural Practices (VietGAP) on farming and trading practices in the dragon fruit supply chain of Vietnam. One of that project’s main intervention is to provide certification to farms conditional on satisfying several requirements – pesticide residue testing is one of them. In the context of the project as well as what has been normally practiced, there is no designated pesticide test center for VietGAP certification and farmers can choose from several certified institutions ranging from local government laboratories to private laboratories in major cities.

In this project, the intervention will assign farmers to specific laboratories to conduct pesticide residue testing. Farmers will be informed about pesticide testing and their lab assignments one month before the date of sample collection, or harvest date. To collect test samples, specialists will visit farms on the scheduled date and, upon collection, directly send the samples to the laboratories. To test for difference in performance by testing agency, dragon fruit samples from the same farm will be sent to multiple labs. Surveys will be administered to farmers, intermediaries, and consumers (end-users) to elicit their beliefs on product quality, certificates, and pesticide residue testing.
Intervention Start Date
Intervention End Date

Primary Outcomes

Primary Outcomes (end points)
Primary outcomes: Laboratory test results on pesticide residue analysis; Buyer’s belief on product quality and willingness to pay
Primary Outcomes (explanation)

Secondary Outcomes

Secondary Outcomes (end points)
Secondary Outcomes (explanation)

Experimental Design

Experimental Design
I plan to conduct a field experiment with dragon fruit farmers in Vietnam. Farmers will be randomly assigned to one of three pesticide testing agencies (each testing agency consisting a treatment arm) and informed about the pesticide test and test agency assignment during the main growing season. Right before the harvest, agricultural specialists will visit farms to collect the samples and provide them to the laboratory assigned to each farmer. Moreover, samples will be sent to multiple test labs to compare performance across different test agencies.
Experimental Design Details
Randomization Method
I will use a computer in my office to conduct random sampling based on treatment status for another project and data collected from its baseline survey.

Randomization Unit
The randomization unit is farmer group (which is at the sub-commune level). For pesticide testing, farmers are randomly sampled from each farmer group.
Was the treatment clustered?

Experiment Characteristics

Sample size: planned number of clusters
88 farmer groups
Sample size: planned number of observations
264 farmers
Sample size (or number of clusters) by treatment arms
Approximately 30 farmer groups per treatment arm (testing agency)
Minimum detectable effect size for main outcomes (accounting for sample design and clustering)
Using incident of pesticide detection from dragon fruit sample as the primary outcome measure, holding the sample size of each treatment group at 80 farmers and significance level at 0.05, the minimum detectable effect size with statistical power of 0.80 and 0.90 is 0.14 and 0.16, respectively, from a baseline of 0.5.

Institutional Review Boards (IRBs)

IRB Name
Human Research Ethics Committee, University of Hong Kong
IRB Approval Date
IRB Approval Number


Post Trial Information

Study Withdrawal

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Is the intervention completed?
Intervention Completion Date
January 31, 2023, 12:00 +00:00
Data Collection Complete
Data Collection Completion Date
January 31, 2023, 12:00 +00:00
Final Sample Size: Number of Clusters (Unit of Randomization)
251 farmers
Was attrition correlated with treatment status?
Final Sample Size: Total Number of Observations
251 farmers
Final Sample Size (or Number of Clusters) by Treatment Arms
Agency A (private) - 82; Agency B (state) - 84; Agency C (parastatal) - 85
Data Publication

Data Publication

Is public data available?

Program Files

Program Files
Reports, Papers & Other Materials

Relevant Paper(s)

Reports & Other Materials