Improving healthy eating in children: Experimental evidence

Last registered on October 08, 2018


Trial Information

General Information

Improving healthy eating in children: Experimental evidence
Initial registration date
October 06, 2018

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
October 08, 2018, 12:20 AM EDT

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



Primary Investigator

Georgetown University Qatar

Other Primary Investigator(s)

PI Affiliation
University of Exeter
PI Affiliation
NYU Abu Dhabi
PI Affiliation
PI Affiliation
University of California Santa Barbara

Additional Trial Information

On going
Start date
End date
Secondary IDs
This paper proposes an experimental approach to incentivize children to make healthier food choices at school. We align children’s appraisal of food choices with their appraisal of schoolwork by introducing a system in which food items are graded based on their nutritional value. We also involve parents and classmates as change agents, providing them with information regarding the food choices of their children/friends.
External Link(s)

Registration Citation

Charness, Gary et al. 2018. "Improving healthy eating in children: Experimental evidence." AEA RCT Registry. October 08.
Former Citation
Charness, Gary et al. 2018. "Improving healthy eating in children: Experimental evidence." AEA RCT Registry. October 08.
Experimental Details


We propose an innovative way of encouraging children to make healthier food choices. We will examine whether providing children with easy-to-understand information about the nutritional value of food items has a durable effect on their food choices. To this end, we introduce a “grading system” – akin to the one used to evaluate academic work – in which food choices during school lunchtime are assessed according to their nutritional content, based on a nutritionist’s expert judgement. The advantage of this approach vis-à-vis alternative interventions is that children are familiar with the grading system used to assess their schoolwork, and will thus be able to clearly understand what it means for their food choices to be satisfactory or not – i.e., to “fail” or “pass” - given the mark they receive.
Intervention Start Date
Intervention End Date

Primary Outcomes

Primary Outcomes (end points)
The primary outcome is to test the hypothesis that children make healthier choices when they receive easy-to-understand information about the nutritional value of the food they choose, compared to the case in which they do not receive this information.
Primary Outcomes (explanation)

Secondary Outcomes

Secondary Outcomes (end points)
As secondary outcomes we will test the following hypotheses.
Hypotheses 2: Providing parents with information about the “quality” of their children’s food choices has a stronger and more prolonged effect on such choices than releasing this information to the children only.
Hypothesis 3: The effectiveness and duration of the incentives’ effects will depend on how the members of a pupil’s social network respond to these incentives.
Hypothesis 4: The effect of the different incentives remains after some time and once incentives had been removed.
Secondary Outcomes (explanation)

Experimental Design

Experimental Design
Our experimental design consists of four different treatments:
Baseline: Children participating in the experiment are presented with five different food trays. Each tray includes five different food items of similar nutritional value, selected by a nutritionist. Subjects have to pick four food items from any of the trays. They have the possibility of choosing items from the same or from different trays, and are able to select more than one item from the same tray and more than one unit of the same item.
Grades Treatment (GT, hereafter): Similar to Baseline, with the difference that students see labels with a “grade” associated with each of the five trays before making their choice. The grades corresponding to each tray depend on their nutritional content, and are analogous to those used to mark children’s academic schoolwork (in Spanish schools grades range from 0 to 10, so the five trays have assigned marks of 0, 2.5, 5, 7.5, and 10, respectively). All the items included in a given tray have the same grade assigned. These grades are the only pieces of information that children allocated to this treatment receive.
Parents Treatment (PT, hereafter): Similar to GT, with the difference that parents receive information about the average mark (linked to the nutritional composition) of their child. Before selecting the items, children are aware of the fact that their parents would receive a report about their “performance”. Note that parents do not receive exact information about children choices, but just the average grade obtained.
Nutritionist Treatment (NT, hereafter): Similar to Baseline, with the difference that the first day of the experiment and before children make their decisions, a nutritionist give a short talk explaining the benefits of eating in a healthy way. Note that the nutritionist give a general talk for all the participants and he avoids leading children to pick any particular item from the trays.
Each day of the intervention in each school, experimental subjects belonging to the same class are gathered in a room (Room A). Participants are not given any information about the experiment. Each student is then – independently and sequentially - asked to move to another room (Room B) in the company of one of the experimenters. In this second room, the subject is walked through a short orientation session - the details of which depend on the subject’s treatment assignment. Next, the student pick the four food items they prefer. Finally, the subject is taken to a third room (Room C), where she joins other classmates who already completed the task. This procedure ensures that individuals’ decisions are not directly influenced by their classmates (who remain either in Room A or C at the time the participant is choosing her lunch in Room B).
Subjects’ dietary choices and grades are recorded by a member of the research team, who is present during the decision process. Note that in order to minimize the interaction with the participants, children make their decisions alone. The bags used to keep the food are transparent so the researcher can see what children pick through it, without being directly involved during the decision.
A staff member of each school is present in Room C where children gather together after making their choices. This member controls that no food is wasted.
To analyze the dynamics and long-term effects of the incentives, we collect data twice a week over three weeks, for a total of 6 observations per subject. In the case of students assigned to PT, information about grades is also sent to their parents. To that end, and in order to keep the same conditions across treatments, prior to the experiment, the parents of all the participants (regardless the treatment) receive the same explanations/clarifications and are requested to provide their contact details before the beginning of the experiment. Parents in PT receive the information only once at the end of each week, which implies that each time they receive the information from two different dates.
After the end of the experiment children are administered a questionnaire asking them to identify their closest friends in class. We also conduct post-experiment questionnaires with children, teachers and parents in order to obtain information about participants’ socioeconomic variables and self-control indicators. Regarding the socioeconomic background of the student, we borrow a questionnaire administered by the Spanish Government. Among the set of variables, we can find: i) the highest educational level achieved by the parents, ii) parents’ jobs, iii) number of books in the household, iv) proxy variables for the economic level of the household, v) parents’ involvement in the school-related activities (homework) of their child. For the self-control indicators, following Tsukayama, Duckworkth and Kim (2013), we include questions related to interpersonal impulsivity and also to schoolwork impulsivity. Finally, in the questionnaire administered to the teachers, we gather information regarding students’ average performance in class, average attendance to the school, and an external measurement of self-control.
Finally, four months after the end of the first intervention, all subjects participate in a second round of the Baseline. The aim of this is to study whether the effect of the different incentives remains after some time and once incentives had been removed.
Experimental Design Details
Randomization Method
Cluster randomization
Randomization Unit
Was the treatment clustered?

Experiment Characteristics

Sample size: planned number of clusters
12 schools
Sample size: planned number of observations
300 students and 7 observations per student, for a total of 2,100 observations
Sample size (or number of clusters) by treatment arms
75 students in baseline, 75 students in "GT", 75 students in "NT", and 75 students in "PT"
Minimum detectable effect size for main outcomes (accounting for sample design and clustering)
Given the estimated ICC, the minimum detectable unconditional effect size for the main outcome vis-à-vis the baseline s is 0.86 for α=0.05 and β=0.8. With the inclusion of covariates, the minimum detectable size for the same parameters is 0.57

Institutional Review Boards (IRBs)

IRB Name
American University of Sharjah Institutional Review Board
IRB Approval Date
IRB Approval Number


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Data Collection Complete
Data Publication

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Program Files

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Reports, Papers & Other Materials

Relevant Paper(s)

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