Evaluating a Marketing Campaign to Increase Participation in School Meals
Phase: NA
Conditions: Nutrition, Healthy
Sponsor: Stanford University

Complete Title: Evaluating a Marketing Campaign to Increase Participation in School Meals   
Short Title: Increasing School Meal Participation 
Protocol Date: July 19, 2024 
NCT #:   NCT06419218 
 
Study Principal Investigator:  
Anna H. Grummon  
Stanford University 
email: agrummon@stanford.edu  
 
 
  
 
 

Introduction 
The goal of these analyses is to examine whether parental exposure to a social media 
campaign encouraging school meal participation increases the frequency with which children eat 
school lunch and school breakfast. This analysis plan pre-specifies the analyses before collecting 
data and therefore serves as our ex-ante planned analysis.  
 
Study Protocol 
Participants will complete a randomized controlled trial. After providing informed 
consent, participants will take a baseline survey programmed in Qualtrics. At the end of the 
survey, participants will be randomized to 1 of 2 arms: 1) school meal campaign or 2) control 
campaign (focused on reading, a neutral topic unrelated to school meals). In the school meal 
campaign arm, participants will be asked to join a private Facebook group where they will view 
messages about the benefits of children eating school meals. In the control arm, participants will 
be asked to join a private Facebook group where they will view messages about the benefits of 
their children reading (a neutral topic unrelated to school meals). In both arms, researchers will 
post messages to the private Facebook groups approximately twice per week for 6 weeks. After 
the 6-week campaigns end, participants in both arms will take a follow-up survey programmed in 
Qualtrics. 
 
Statistical Considerations 
General Principles  
Primary analyses will be intent-to-treat, including all randomized participants regardless 
of whether they joined a Facebook group or completed the follow-up survey. Depending on the 
proportion of participants who join the Facebook groups, we may consider conducting 
secondary, per-protocol analyses including only participants who joined a Facebook group.  
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.  
 
Outcome Measures 
Table 1 describes the outcome measures. 

Table 1. Outcome measures 
Outcome 
Description 
Timing of Assessment 
Co-primary outcomes 
 
 
Children’s consumption of school 
lunches 
Parental report of the usual number of days per week their child ate school 
lunch during the past month. Assessed with 1 item: “Thinking about the last 
month, how many days a week did your child usually eat school lunch?” This 
item will be scored on a 6-point scale from "0 days per week" (0) to "5 days 
per week" (5).  
Collected in a ~10 minute 
survey at baseline and again 
at 6 weeks. 
Children’s consumption of school 
breakfasts 
Parental report of the usual number of days per week their child ate school 
breakfast during the past month. Assessed with 1 item: Thinking about the 
last month, how many days a week did your child usually eat school 
breakfast?” This item will be scored on a 6-point scale from "0 days per 
week" (0) to "5 days per week" (5). 
Collected in a ~10 minute 
survey at baseline and again 
at 6 weeks. 
Secondary outcomes 
 
 
Campaign reactions 
 
 
Noticing the school meal campaign 
Parental report of whether they noticed the school meal campaign. Assessed 
with 1 item: “In the last 6 weeks, have you seen any messages or advertising 
on Facebook encouraging children to eat school lunch or school breakfast?” 
Response options are “yes” (1) and “no” (0).   
Collected in a ~10 minute 
survey at 6 weeks. 
Number of school meals campaign 
topics recognized 
Parental report of the number of topics they recognize having seen in 
messages about school meals. Assessed with 1 item: “Which of these topics 
did the messages discuss, if any? Check all that apply.” Response options list 
8 topics plus options for “none of these” and “not sure.” Number of topics 
recognized will be calculated as the sum of all topics that parents indicate 
they have seen. Those who answer, “none of these” and “not sure” will be 
coded as recognizing 0 topics. Those who report not noticing the school meal 
marketing campaign will be coded as recognizing 0 topics.   
Collected in a ~10 minute 
survey at 6 weeks. 
Frequency of reading campaign 
messages 
 
Parental report of the frequency with which they read their assigned campaign 
messages. Assessed with 1 item: “In the past month, how often did you read 
these messages?” This item will be scored on a 5 point scale ranging from 
“Never or less than 1 time per week” (1) to “Every day or more often” (5).  
Collected in a ~10 minute 
survey at 6 weeks. 

Outcome 
Description 
Timing of Assessment 
Social interactions about campaign 
Parental report of the frequency with which they talked to others about their 
assigned campaign messages. Assessed with 1 item: “In the last month, how 
often did you talk to others about these messages?” This item will be scored 
on a 5 point scale ranging from “Never or less than 1 time per week” (1) to 
“Every day or more often” (5). 
Collected in a ~10 minute 
survey at 6 weeks. 
Social interactions about school 
meals 
Parental report of the frequency with which they talked to others about school 
meals. Assessed with 3 items (e.g., “In the last month, how often did you talk 
to others about school meals?”). Response options are on a 5-point scale 
ranging from “Never or less than 1 time per week” (1) to “Every day or more 
often” (5). Responses to the 3 items will be averaged to create a mean score.   
Collected in a ~10 minute 
survey at 6 weeks. 
Perceived benefits of school meals  
 
Perceived benefits of school lunch 
Parental report of the benefits of their child consuming school meals. 
Assessed with 8 items (e.g., “My child eating school lunch helps my child do 
well in school”). Response options are on a 5-point scale ranging from 
“Strongly disagree” (1) to “Strongly agree” (5). Responses to the 8 items will 
be averaged to create a mean score. 
Collected in a ~10 minute 
survey at baseline and again 
at 6 weeks. 
Perceived benefits of school 
breakfast 
Parental report of the benefits of their child consuming school meals. 
Assessed with 8 items (e.g., “My child eating school breakfast helps my child 
do well in school”). Response options are on a 5-point scale ranging from 
“Strongly disagree” (1) to “Strongly agree” (5). Responses to the 8 items will 
be averaged to create a mean score. 
Collected in a ~10 minute 
survey at baseline and again 
at 6 weeks. 
Knowledge that school meals are 
free 
 
 
Knowledge that school lunch is free Parental knowledge that lunches served at their child’s school are free to all 
students. Assessed with 1 item: “Are school lunches free for all students at 
your child’s school?” Response options “yes” (coded as 1) and “no” or “not 
sure” (both coded as 0).   
Collected in a ~10 minute 
survey at baseline and again 
at 6 weeks. 
Knowledge that school breakfast is 
free 
Parental knowledge that breakfasts served at their child’s school are free to all 
students. Assessed with 1 item: “Are school breakfasts free for all students at 
your child’s school?” Response options “yes” (coded as 1) and “no” or “not 
sure” (both coded as 0).   
Collected in a ~10 minute 
survey at baseline and again 
at 6 weeks. 

Outcome 
Description 
Timing of Assessment 
Perceived healthfulness of school 
meals  
 
 
Perceived healthfulness of school 
lunch 
Parental perception of the healthfulness of the lunches served at their child’s 
school. Assessed with 1 item: “How healthy or unhealthy are the school 
lunches at your child’s school?” Response options are on a 5-point scale 
ranging from “Very unhealthy” (1) to “Very healthy” (5).  
Collected in a ~10 minute 
survey at baseline and again 
at 6 weeks. 
Perceived healthfulness of school 
breakfast 
Parental perception of the healthfulness of the breakfasts served at their 
child’s school. Assessed with 1-item: “How healthy or unhealthy are the 
school breakfasts at your child’s school?” Response options are on a 5-point 
scale ranging from “Very unhealthy” (1) to “Very healthy” (5). 
Collected in a ~10 minute 
survey at baseline and again 
at 6 weeks. 
Behavioral intentions  
 
 
Intentions to encourage their 
children’s consumption of school 
lunch 
 
Parental report of the likelihood of encouraging their child to eat school lunch 
in the next month. Assessed with 1 item: “In the next month, how likely are 
you to encourage your child to eat school lunch?”  Response options are on a 
5-point scale ranging from “Not at all likely” (1) to “Extremely likely” (5). 
 
Collected in a ~10 minute 
survey at baseline and again 
at 6 weeks. 
Intentions to encourage their 
children’s consumption of school 
breakfast 
 
Parental report of the likelihood of encouraging their child to eat school 
breakfast in the next month. Assessed with 1 item: “In the next month, how 
likely are you to encourage your child to eat school breakfast?”  Response 
options are on a 5-point scale ranging from “Not at all likely” (1) to 
“Extremely likely” (5). 
 
Collected in a ~10 minute 
survey at baseline and again 
at 6 weeks. 
Barriers to participation 
 
 
Barriers to children’s school lunch 
consumption 
Parental report of the barriers preventing their child from eating school lunch. 
Assessed with 1 item: “What are some reasons that your child doesn’t eat 
school lunch more often? Check all of the reasons that apply.”  
Response options list 15 reasons plus “NA - my child eats school lunch every 
day or almost every day” and a free response option for “other.” Total number 
of barriers selected will be summed. Those who report “NA - my child eats 
school lunch every day or almost every day” will be coded as having 0 
barriers.   
Collected in a ~10 minute 
survey at baseline and again 
at 6 weeks. 

Outcome 
Description 
Timing of Assessment 
Barriers to children’s school 
breakfast consumption 
Parental report of the barriers preventing their child from eating school 
breakfast. Assessed with 1 item: “What are some reasons that your child 
doesn’t eat school breakfast more often? Check all of the reasons that apply.”  
Response options list 16 reasons plus “NA - my child eats school breakfast 
every day or almost every day” and a free response option for “other.” Total 
number of barriers selected will be summed. Those who report “NA - my 
child eats school breakfast every day or almost every day” will be coded as 
having 0 barriers.   
Collected in a ~10 minute 
survey at baseline and again 
at 6 weeks. 
Food insecurity 
 
 
Household food insecurity 
Parental report of household food insecurity. Assessed with 6 items (e.g., “In 
the last month, were you ever hungry but didn't eat because there wasn't 
enough money for food?”) Response options include “no” or “yes”; “never 
true”, “sometimes true”, or “often true”; “only 1 or 2 days,” “some days but 
not every day,” or “almost every day.” Responses of “often” or “sometimes” 
and “yes” are coded as affirmative (yes). Likewise, responses of “almost 
every day” and “some days but not every day” are coded as affirmative (yes). 
The sum of affirmative responses to the six questions in the module is the 
household’s raw score on the scale. 
Household food security status is assigned as follows: 
Raw score 0-1—High or marginal food security  
Raw score 2-4—Low food security  
Raw score 5-6—Very low food security 
Analyses will dichotomize households into those with high or marginal food 
security and those with low or very low food security.  
 
 
Collected in a ~10 minute 
survey at baseline and again 
at 6 weeks. 

Outcome 
Description 
Timing of Assessment 
Child food insecurity 
Parental report of child food insecurity. Assessed with 8 items (e.g., “In the 
last month, did you ever cut the size of your child's meals because there 
wasn't enough money for food?”) Response options include “no” or “yes”; 
“never true”, “sometimes true”, or “often true”;  “only 1 or 2 days,” “some 
days but not every day,” or “almost every day.” Responses of “often” or 
“sometimes” and “yes” are coded as affirmative (yes). Responses of “almost 
every day” and “some days but not every day” are coded as affirmative (yes). 
The sum of affirmative responses to the 8 questions in the module is the 
child’s raw score on the scale. 
Child food security status is assigned as follows: 
Raw score 0-1—High or marginal food security among children 
Raw score 2-4—Low food security among children 
Raw score 5-8—Very low food security among children 
Analyses will dichotomize households into those with children with high or 
marginal food security and those with children with low or very low food 
security.  
 
 
Collected in a ~10 minute 
survey at baseline and again 
at 6 weeks. 
 
 
 
 

Data Preparation 
 
To prepare the data, we will examine all scales to ensure they achieve adequate internal 
consistency (Cronbach’s α>0.70), dropping items as needed to improve internal consistency. If we are 
unable to achieve adequate internal consistency by dropping items, we may exclude the unreliable scales 
from analyses (e.g., not analyze treatment effects on these outcomes). 
 
Statistical Methods 
1. Analyses of the co-primary outcomes: 
a. We will use mixed effects regression models to evaluate the effect of the school meals 
campaign on children’s school lunch consumption and children’s school breakfast 
consumption. In separate models for lunch and breakfast, we will regress usual number 
of school meals eaten per week on an indicator variable for trial arm (school meal 
campaign vs. control), an indicator variable for time period (baseline vs. follow-up) and 
the interaction between trial arm and time period. The treatment effect is given by the 
coefficient on the interaction term. We will consider linear or Poisson models, based on 
the distribution of the outcome and model fit. We will treat the intercept as random to 
account for repeated measures within participants and will include state fixed effects.  
b. To examine the potential differential effects of the school meals campaign by 
demographic characteristics, analyses will examine whether the effect of the school 
meals campaign on children’s school lunch consumption and children’s school breakfast 
consumption is modified by household income (≤ vs. >185% Federal Poverty Level) or 
parent’s race/ethnicity (with categories determined based on distribution of race/ethnicity 
in the sample). We will test for effect modification by adding to the primary model three-
way interactions (i.e., difference-in-difference-in-differences) between trial arm, time 
period, and variable(s) for the potential effect modifier, using separate models for each 
outcome (school lunch consumption and school breakfast consumption) and effect 
modifier (income and race/ethnicity).  
 
2. Analyses of the secondary outcomes: 
a. We will use a similar mixed effects regression approach to evaluate the effect of the 
school meals campaign on secondary outcomes (e.g., perceived benefits of school 
meals, knowledge and attitude about school meals, behavioral intentions, perceived 
barriers to school meal participation, and food insecurity). We will use mixed effects 
logistic regression for binary outcomes, mixed effects linear regression for continuous 
outcomes, and mixed effects Poisson regression for count outcomes.  We will treat the 
intercept as random to account for repeated measures within participants. For outcomes 
measured only at follow-up (e.g., noticing), we will use linear, logistic, or Poisson 
regression.  
 
Sample Size Needs 

We estimated power using G*Power 3.1.1 No published studies have examined the effect of 
parent-directed school meal marketing campaigns on children’s school meal consumption,2 so we 
powered to detect a small standardized effect (Cohen’s f=0.05, equivalent to d=0.10).3 We assumed 75% 
of the initial sample of 800 parents would complete the follow-up survey (similar retention to a previous 
study using similar methods4), yielding an analytic sample of n=600. Assuming alpha=0.05 and a 
correlation among repeated measures of 0.60 (based on prior research5), a sample of this size would 
yield 80% power to detect an effect of school meal campaign on consumption of school lunch and 
consumption of school breakfast of f=0.05 or larger. Our prior studies with parents suggest that 
messaging interventions are likely to yield effects of this size or larger.6-8 Additionally, studies of child-
directed school meal marketing campaigns9 and multicomponent interventions that include 
marketing10,11 suggest effects of this size are reasonable. 
 
Exclusions and Outliers 
We will exclude participants who do not consent or do not complete the baseline survey, as these 
participants will not be randomized. Primary analyses will be intent-to-treat, including all randomized 
participants regardless of whether they join their assigned Facebook group or complete the follow-up 
survey. We will also consider conducting a secondary analysis per-protocol, examining only those who 
joined their assigned Facebook group and completed the follow-up survey.  
 

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