Everyday Research Methods

California high schoolers eat fewer calories...

This recent report from the New York Times focuses on California's high school students. About five years ago, the state banned junk foods like soda, chips, and candy from high schools in the state. Now a study has reported that California students eat fewer calories than students in other states.

The study found that California high school students consumed on average nearly 160 calories fewer per day than students in other states, the equivalent of cutting out a small bag of potato chips.

To study the effect of this policy, the researchers examined data from the Centers for Disease Control and Prevention on the eating habits of high school students in California, comparing it with data on students from 14 states that did not have nutrition standards for vending machine snacks and other foods sold outside of school lunches and other meal plans.

a) This study's design seems to be a quasi-experiment. What makes it so?

b) Sketch a graph of the study and its results.

c) What internal validity threats might be present in this study? If you were the researcher, what would you do to control for these threats?

d) Overall, do you think the evidence presented here supports the claim that banning junk food in schools can help kids eat fewer calories?

Suggested Answers

a) This is a quasi experiment--probably a nonequivalent groups, post-test only design. It is a quasi experiment because the independent variable (being in a state that bans junk food in school) is not manipulated. Students cannot be randomly assigned to live in a state with a junk food ban (i.e., CA) or to a state without junk food ban (i.e., the other 14 states).

b) Your sketch would probably have "Calories consumed daily" on the y-axis and "state" on the x-axis. On the x-axis you could plot all 15 states separately (showing CA with the lowest calorie consumption), or you could plot California and an average of the remaining 14 states (showing CA with the lowest calorie consumption).

c) We might worry that compared to the other 14 states in the study, CA students come disproportionately from one ethnic background (for example, there are more Hispanic students there), or that CA and the comparison states may also have different requirements for physical education in school, which might affect eating habits. To find out how the researchers controlled for these factors, you could check the original source in the Archives of Pediatrics and Adolescent Medicine.

d) If, after reading the original report, you were convinced that the junk food ban was the only "active ingredient" separating CA from the 14 comparison states, then you might well be convinced that the junk food ban is playing a role in controlling child and adolescent obesity.

Should we stop calling people "consumers?"

Time magazine presents a story this month about a line of research on materialism. The full story is accessible here.

One of the studies conducted by the research team, led by psychologist Galen Bodenhausen, was on the effect of calling people "consumers" versus "individuals."

In one of the study’s tests, participants were presented with the following hypothetical scenario: There is a water shortage, and four people (including the participants) must share a well. Sometimes in the experiment, participants were called “consumers,” and other times they were referred to as “individuals.” And apparently, words can be powerful.

The “consumers” rated themselves as less trusting of others to conserve water, less personally responsible and less in partnership with the others in dealing with the crisis. The consumer status, the authors concluded, “did not unite; it divided.”

a) In this experiment, what was the independent variable ? What was the dependent variable?

b) Because this is an experiment, you may be able to make a causal claim from this research. What would the causal claim be?

c) What internal validity concerns might you raise about this study? If you were the authors, how would you have ensured internal validity in this experiment?