Message bias and consumer attitudes towards antibiotics in beef and dairy

Last registered on July 28, 2023


Trial Information

General Information

Message bias and consumer attitudes towards antibiotics in beef and dairy
Initial registration date
July 21, 2023

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
July 28, 2023, 10:50 AM EDT

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


Primary Investigator


Other Primary Investigator(s)

PI Affiliation
University of Calgary
PI Affiliation

Additional Trial Information

Start date
End date
Secondary IDs
Prior work
This trial does not extend or rely on any prior RCTs.
In this experiment we examine how an information intervention affects people’s attitudes towards food attributes. Specifically, we focus on antibiotic use in food production. First, we test whether one-sided and two-sided messages affect consumers’ willingness to pay for the antibiotics free premium. Second, we examine the kinds of consumers that are most receptive to either of the messages. We examine factors potentially affecting a consumer's receptivity to the different messages, such as existing subjective and objective knowledge about antibiotics, their scientific literacy, their education level and their cultural attitudes. Finally, we study a potential mechanism through which the messages change people’s preferences. We hypothesize whether a person that delivers a balanced message is perceived as more trustworthy than a person that delivers a biased message and therefore the consumer is more open to contrary positions.
External Link(s)

Registration Citation

Bernedo, Maria, David Lansing and Guillaume Lhermie. 2023. "Message bias and consumer attitudes towards antibiotics in beef and dairy." AEA RCT Registry. July 28.
Experimental Details


Intervention Start Date
Intervention End Date

Primary Outcomes

Primary Outcomes (end points)
1. Premium for antibiotic free products at baseline, i.e. the difference between the willingness to pay (WTP) for the antibiotic free product and the WTP for the product raised using antibiotics
2. Change in the antibiotic free premium: Difference between the antibiotic free premium after the information is provided and the one at baseline
Primary Outcomes (explanation)

Secondary Outcomes

Secondary Outcomes (end points)
Secondary Outcomes (explanation)

Experimental Design

Experimental Design
Our survey will be administered by Qualtrics, an online survey platform. The survey approximately takes 15 minutes to complete.

Sample recruitment criteria
Participants are a population-representative sample that matches the national U.S. composition in terms of the age, gender, income, race, and rural/urban distribution. They are required to be 18 years old or older and eat meat and drink milk. Participants are considered inattentive and dropped from the sample if they meet one or more of the following criteria: (i) they spent 45% of the median time or less on the survey, (ii) provided pattern-based responses in the two matrix shaped cultural worldview questions and (iii) entered impossible height and weight values.

We will pose the survey questions before and after the information treatment. Before the treatment we will ask some socio-demographic questions (age, gender, race, education and income) and a subjective knowledge question. After these questions we will ask people for their willingness to pay (WTP) for products with the antibiotic-free label and without it. The products are ground-beef and milk. The WTP questions are hypothetical and open-ended. After the treatment we will repeat the WTP questions. In total each participant will provide eight WTP values. Additionally, we randomize the order in which the beef and milk questions appear before and after the video.

After the second round of WTP questions we ask additional questions that we believe correlate with the premium or could moderate the treatment effect. We ask these questions at the end to avoid priming participants (Folk and Zimmerman, 2013; Grewenig et al. 2020).

Information treatment
We randomly assign participants to one of the three videos about the use and effects of antibiotics (the positive message, the negative message or the balanced message) or to a control video (see Appendix). The “control video” is about a different topic entirely.
At the beginning of each video we added the same opening chyron that introduced the speaker as a professor of a renowned university (see Appendix). No other reference to sources is mentioned in the videos. By harmonizing the source of the information, we expect that the effect of the message will depend only on its content and not on people’s perception about the quality of the information.
Experimental Design Details
Randomization Method
Randomization done by Qualtrics.
Randomization Unit
We randomize by individual.
Was the treatment clustered?

Experiment Characteristics

Sample size: planned number of clusters
We will not cluster observations.
Sample size: planned number of observations
1,500 individuals
Sample size (or number of clusters) by treatment arms
375 individuals per treatment.
Minimum detectable effect size for main outcomes (accounting for sample design and clustering)
We conducted a power analysis to calculate the minimum detectable effect and sample size to measure the effect of three information messages on the willingness to pay for a premium for antibiotic-free food. Because of budget constraints, we are limited to a sample size of 1,500 individuals. We calculate that with this sample size we can detect a minimal detectable effect of the balance message of 16% and of the biased messages of around 5% each with a power of 0.8.
Supporting Documents and Materials


Document Name
Document Type
Document Description

MD5: ace2c203e01af55ae11d09be79a70c71

SHA1: b5a6a0e0408e2e4a123c746c17376c7fdbfb2f71

Uploaded At: July 21, 2023


Institutional Review Boards (IRBs)

IRB Name
UMBC Institutional Review Board
IRB Approval Date
IRB Approval Number
Analysis Plan

Analysis Plan Documents

Message Bias and Antibiotics, Pre-Analysis Plan

MD5: eaa7bac7fc5bc906420b3c5a84ba61d3

SHA1: edd4e6875fe0b08a442bbf1409ad90fab1cf8c81

Uploaded At: July 21, 2023


Post Trial Information

Study Withdrawal

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Is the intervention completed?
Intervention Completion Date
January 25, 2023, 12:00 +00:00
Data Collection Complete
Data Collection Completion Date
January 25, 2023, 12:00 +00:00
Final Sample Size: Number of Clusters (Unit of Randomization)
Was attrition correlated with treatment status?
Final Sample Size: Total Number of Observations
Final Sample Size (or Number of Clusters) by Treatment Arms
Data Publication

Data Publication

Is public data available?

Program Files

Program Files
Reports, Papers & Other Materials

Relevant Paper(s)

Reports & Other Materials