Encouraging children to eat more fruits and veggies: Experimental design practice

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Eating fruits and vegetables is good for all of us, including growing children. Researchers wondered what caregivers could do to increase fruit and veggie intake among the younger set. Explain to your Intro Psych students that the first thing researchers do is a literature review where we dive into the research databases to find peer-reviewed journal articles on our topic of interest.

If you’d like your students to get practice using your library’s databases, contact your favorite reference librarian for database instructions you can provide your students. Ask students what search terms might yield the best results for this topic. I had success using just ‘vegetables’ and ‘children.’ Explain that researchers first read the article title. If the title sounds relevant to their topic, they’ll read the abstract. If the abstract sounds promising, they’ll read the article—or, rather, they’ll read the parts of the article of greatest interest and not necessarily in order. For example, after the abstract, they may read the discussion, and then go back to the beginning to skim the introduction paying closer attention to the last paragraphs since that’s where the hypotheses are most likely to be, and then carefully read the methods section to learn how the study was done, and, then, finally, read the results.

Give students a few minutes to pop into your library’s databases to search for peer-reviewed articles that identify variables that are associated with children eating more vegetables. The studies may be correlational or experimental. When they find a strategy, ask them to share it.

If you’d like to skip this lit review part, instead share with your students these variables that are associated with children eating more fruits or vegetables: repeatedly giving children a taste of a vegetable (Lakkakula et al., 2010; Wardle et al., 2003), caregivers eating more vegetables (Rasmussen et al., 2006), more shared family meals (Rasmussen et al., 2006), decreased amount of television watching (Rasmussen et al., 2006), decreased incidence of eating fast food (Rasmussen et al., 2006), increased variety of fruits and vegetables available at meals (Just et al., 2012; Roe et al., 2013).

Give students this hypothesis posited by one group of researchers: “children eat more fruits and more vegetables when the regular family mealtime duration is extended” (Dallacker et al., 2023). Ask students to work in small groups to design a study that would test this hypothesis. Students should identify their independent variable—including its conditions and operational definitions for those conditions—and their dependent variable(s)—including operational definition(s). Invite groups to share their experimental designs. Highlight the strengths of each group’s design while also discussing possible shortcomings. Emphasize that there is no one right way to design an experiment. The more ways a hypothesis is studied, the more support we have for the hypothesis.

As a follow-up assignment, ask your students to read the freely available journal article published by a group of researchers in Germany who tested this same hypothesis (Dallacker et al., 2023). Ask students to address these questions:

  1. The primary hypothesis was “children eat more fruits and more vegetables when the regular family mealtime duration is extended.” What was their secondary hypothesis?
  2. What committee provided ethics approval?
  3. Was consent to participate in the study given by the caregiver, the child, or both?
  4. How many parent-child pairs participated in this experiment?
  5. How did researchers figure out how long the regular meal and the intervention meal should be?
  6. What was the experiment’s independent variable? What were the two conditions of the independent variable? How were these operationally defined?
  7. What were the experiment’s dependent variables? How were these operationally defined?
  8. Were the researchers’ primary and secondary hypotheses supported by their data? Explain.



Dallacker, M., Knobl, V., Hertwig, R., & Mata, J. (2023). Effect of longer family meals on children’s fruit and vegetable intake: A randomized clinical trial. JAMA Network Open, 6(4), e236331. https://doi.org/10.1001/jamanetworkopen.2023.6331

Just, D. R., Lund, J., & Price, J. (2012). The role of variety in increasing the consumption of fruits and vegetables among children. Agricultural and Resource Economics Review, 41(1), 72–81. https://doi.org/10.1017/S1068280500004196

Lakkakula, A., Geaghan, J., Zanovec, M., Pierce, S., & Tuuri, G. (2010). Repeated taste exposure increases liking for vegetables by low-income elementary school children. Appetite, 55(2), 226–231. https://doi.org/10.1016/j.appet.2010.06.003

Rasmussen, M., Krølner, R., Klepp, K.-I., Lytle, L., Brug, J., Bere, E., & Due, P. (2006). Determinants of fruit and vegetable consumption among children and adolescents: A review of the literature. Part I: quantitative studies. International Journal of Behavioral Nutrition and Physical Activity, 3(1), 22. https://doi.org/10.1186/1479-5868-3-22

Roe, L. S., Meengs, J. S., Birch, L. L., & Rolls, B. J. (2013). Serving a variety of vegetables and fruit as a snack increased intake in preschool children,,. The American Journal of Clinical Nutrition, 98(3), 693–699. https://doi.org/10.3945/ajcn.113.062901

Wardle, J., Cooke, L. J., Gibson, E. L., Sapochnik, M., Sheiham, A., & Lawson, M. (2003). Increasing children’s acceptance of vegetables; a randomized trial of parent-led exposure. Appetite, 40(2), 155–162. https://doi.org/10.1016/S0195-6663(02)00135-6




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About the Author
Sue Frantz has taught psychology since 1992. She has served on several APA boards and committees, and was proud to serve the members of the Society for the Teaching of Psychology as their 2018 president. In 2013, she was the inaugural recipient of the APA award for Excellence in the Scholarship of Teaching and Learning at a Two-Year College or Campus. She received in 2016 the highest award for the teaching of psychology--the Charles L. Brewer Distinguished Teaching of Psychology Award. She presents nationally and internationally on the topics of educational technology and the pedagogy of psychology. She is co-author with Doug Bernstein and Steve Chew of Teaching Psychology: A Step-by-Step Guide, 3rd ed. and is co-author with Charles Stangor on Introduction to Psychology, 4.0.