Consumer Responses to Alcohol Warnings
Phase: NA
Conditions: Alcohol Drinking
Sponsor: Stanford University

Complete Title: Consumer Responses to Alcohol Warnings 
Short Title: Consumer Responses to Alcohol Warnings 
Protocol Date: October 3, 2023 
NCT #: NCT06159647 
 
Study Principal Investigator:  
Anna H. Grummon  
Department of Pediatrics 
3145 Porter Drive, A103 
Palo Alto, CA 94304 
Phone 650-644-7366  
email: agrummon@stanford.edu  
 
 
  
 
 

Protocol Synopsis  
 
Study Title 
Consumer Responses to Alcohol Warnings 
Funder 
NA 
Clinical Phase 
NA 
Study Rationale 
• Policymakers and public health organizations are increasingly 
interested in communicating alcohol’s harms to the public, 
including through mandated warning labels as well as mass media 
campaigns.  
• Communicating alcohol’s harms could increase consumer 
understanding of these harms and reduce alcohol consumption and 
alcohol-related health harms.   
• Alcohol contributes to more than 200 health harms, giving 
policymakers and public health organizations many options to 
choose from when selecting topics to include in messages about 
alcohol-related harms.  
• However, it remains unknown which of these topics should be 
prioritized in communication efforts.   
Study 
Objective(s) 
Primary  
• To evaluate whether alcohol warnings about different topics elicit 
higher perceived message effectiveness than control messages.  
 
Secondary 
• To evaluate whether alcohol warnings about different topics elicit 
higher reactance than control messages.   
Study Design 
 
Randomized experiment.  
Subject 
Population 
key criteria for 
Inclusion and 
Exclusion: 
Inclusion Criteria 
1. Age 21 and older 
2. Reside in the United States 
3. Able to complete a survey in English 
Exclusion Criteria 
1. Under the age of 21 
2. Reside outside of the United States 
3. Unable to complete a survey in English 
Number of 
Subjects  
2,500 
Study Duration 
Each subject’s participation will last approximately 10 minutes. 
The enrollment period is expected to last ~1-2 weeks. 

Study Phases 
  
There are two phases: 
(1) Screening: screening for eligibility and obtaining consent and  
(2) Intervention: study intervention/experimental treatment. 
Efficacy 
Evaluations 
The primary outcome is perceived message effectiveness for discouraging 
alcohol consumption. It is measured with 1 item adapted from prior 
studies.  
Statistical and 
Analytic Plan 
Primary outcome 
• We will use linear mixed models to examine the effect of each 
alcohol warning topic on perceived message effectiveness 
compared to control topics.  
 
Secondary outcomes 
• We will use linear mixed models to examine the effect of each 
alcohol warning topic on message reactance compared to control 
topics.  
 
Data and Safety 
Monitoring Plan 
• The principal investigator is responsible for data quality 
management and ongoing assessment of safety.   
 
 

Introduction 
The goal of the analysis described here is to use data we collected through an online 
randomized experiment to examine consumer responses to alcohol warning messages about 
different topics. This analysis examines the effects of warning topic (e.g., mouth cancer, liver 
damage) on perceived message effectiveness (primary outcome) and message reactance 
(secondary outcome).  
This analysis plan pre-specifies the analyses before collecting data and therefore serves as 
our ex-ante planned analysis.  
 
Study Protocol 
Participants will complete an online randomized experiment programmed in Qualtrics. 
After providing informed consent, participants will view and rate messages on perceived 
message effectiveness (primary outcome) and message reactance (secondary outcome). 
Participants will be randomly assigned to 1 of 4 topic sets. Each topic set includes messages 
about 6 different topics: 5 warning topics and 1 control topic. (The warning topics vary across 
topic sets, but the control topic is the same across all topic sets). Participants will view messages 
about these topics in random order. Participants will view and rate 2 messages per topic (shown 
in random order within topic), for a total of 12 messages.  
 
Statistical Considerations 
General Principles  
We will use a two-sided critical alpha of 0.05 to conduct all statistical tests. All 
confidence intervals presented will be 95% and two-sided. Analyses of the primary and 
secondary outcomes will include all randomized participants according to experimental 
conditions they were randomized to (i.e., intent-to-treat). We will use complete case analysis to 
handle any missing data in analyses of the primary and secondary outcomes. 
Primary Outcome 
The primary outcome is perceived message effectiveness for discouraging alcohol 
consumption. We will measure perceived message effectiveness with 1 item adapted from prior 
studies: “How much does this message discourage you from wanting to drink alcohol?” 
Response options will range from not at all (1) to a great deal (5).  
Hypothesis 1. We hypothesize that all alcohol warning topics receive higher perceived 
message effectiveness ratings than the control topic.  
Secondary Outcome 
The secondary outcome is message reactance. We will measure message reactance with 1 
item adapted from prior studies: “This message exaggerates the health effects of alcohol.” 
Response options will range from strongly disagree (1) to strongly agree (5). 
Hypothesis 2. We hypothesize that that all alcohol warning topics receive higher message 
reactance ratings than the control topic.  
Statistical Methods 

1. Analyses of the primary outcome: 
a. We will use linear mixed models to evaluate the effect of each alcohol warning 
topic compared to the control topic on the primary outcome of perceived 
message effectiveness. We will regress perceived message effectiveness on a set 
of indicator variables representing each alcohol warning topic (e.g., mouth cancer, 
throat cancer, breast cancer, etc.), excluding the control topic as the referent. We 
will treat the intercept as random to account for repeated measures within 
participants. The coefficients on the alcohol warning topics give the average 
difference in mean perceived message effectiveness between each warning topic 
and the control topic. Hypothesis 1 will be supported if all coefficients on the 
alcohol warning topics are positive and statistically significant. Given the 
exploratory nature of the study, we do not plan to adjust p-values for multiple 
comparisons.  
b. In addition to testing Hypothesis 1, we will also descriptively rank the alcohol 
warning topics on the primary outcome of perceived message effectiveness. We 
will estimate mean perceived message effectiveness for each alcohol warning 
topic (averaging across messages for each topic) and rank those means.  
c. Finally, we will descriptively rank the alcohol warning messages on the 
primary outcome of perceived message effectiveness. We will estimate means for 
each alcohol warning message and rank those means.  
2. Analyses of the secondary outcome: 
a. We will use linear mixed models to evaluate the effect of each alcohol warning 
topic compared to the control topic on the secondary outcome of message 
reactance. We will use the same approach as for the primary outcome (see no. 1 
above).  
b. We will descriptively rank the alcohol warning topics on the secondary 
outcome of message reactance. We will estimate mean reactance for each alcohol 
warning topic (averaging across messages for each topic) and rank those means.  
c. We will descriptively rank the alcohol warning messages on the secondary 
outcome of message reactance. We will estimate mean reactance for each alcohol 
warning message and rank those means.  
 
We do not plan to conduct moderation analyses.  
 
 
Sample Size and Power 
We plan to collect data from ~2,500 participants (~625 per topic set). We used G*Power to 
estimate sample size needs.1 We estimated power to detect an effect of each warning topic vs. the 
control topic assuming an alpha=0.05 and correlation among repeated measures of 0.6 (based on 
a prior study of alcohol warnings2). We estimated power assuming 2 repeated measures, 
reflecting that our contrast of interest has two within-subjects levels (warning topic vs. control). 

Under these assumptions, our sample size will yield 80% power to detect a small standardized 
effect of Cohen’s f=.05 (or Cohen’s d=.10) or larger of each warning topic vs. the control topic. 
A prior study of alcohol warning topics found effects of this size or larger when comparing 
perceived message effectiveness of alcohol warning topics vs. control topics.2   
 
Exclusions and Outliers 
We will exclude participants who do not complete the survey or who complete the survey 
implausibly quickly (defined as <1/3 of the median completion time).  
 

References 
 
1. Faul F, Erdfelder E, Lang AG, Buchner A. G*Power 3: A flexible statistical power analysis 
program for the social, behavioral, and biomedical sciences. Behavior Research Methods. 
2007;39(2):175-191. doi:10.3758/BF03193146 
2. Grummon AH, Ruggles PR, Greenfield TK, Hall MG. Designing effective alcohol warnings: 
Consumer reactions to icons and health topics. Am J Prev Med. Published online 2022. 
doi:https://doi.org/10.1016/j.amepre.2022.09.006