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Quasi experiment: Food mind-set

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  • Quasi experiment: Food mind-set

The following is a sample Paper 3 that looks at a quasi-experiment. Below you will first find the stimulus piece, followed by the static questions.  A copy of the mock paper is included to give students as an in-class assessment.

Potential answers are included in the hidden boxes below.

Student copy

Link to the original study

The stimulus piece

One of the cognitive theories of obesity is that people who are overweight or obese are more likely to notice and be distracted by food.  This is known as an attentional bias. To test the role of attentional bias for food in overweight and obese people, Kaisari (2018) carried out a quasi-experiment.

The sample was made up of 43 overweight or obese participants and 49 healthy-weight participants. Participants were between 18 - 60 years old. The sample was a self-selected sample, recruited through posters, emails and mass mailings. To reduce demand characteristics, participants were told that it was a study of eating habits and memory. Any participants who had a history of an eating disorder were excluded from the study.

The two groups (overweight vs. not overweight) were exposed to two different conditions. They were either given a "food mindset" in which they were asked to memorize pictures of food items, or a "non-food mindset", where they were asked to memorize images that were not food related - such as a hammer. Then, they were asked to sit at a computer terminal and locate a circle as quickly as they could, while ignoring a distractor (a square). On some trials, the circle was accompanied by a food image; in other trials, the distractor was accompanied by the food image.

All participants found it harder to spot the circle when they were in a food mindset and it was the distractor, rather than the target circle, that was accompanied by an image of food. Crucially, however, the distracting effect of food and being in a food mindset was greater for the overweight or obese participants, suggesting they had a harder time disengaging from food. 

The participants also returned to the lab a year later for a weigh-in. The more that the participants’ task performance had been swayed by a food mindset, the greater their increase in BMI tended to be, indicating that the attentional processes uncovered in the lab have a real-life impact. The researchers argue that thinking about food increases the likelihood of overeating because a person is more responsive to the presence of food in the environment.

References

Kaisari, P., Kumar, S., Hattersley, J., Dourish, C. T., Rotshtein, P., & Higgs, S. (2018). Top-down guidance of attention to food cues is enhanced in individuals with overweight/obesity and predicts change in weight at one-year follow up. International Journal of Obesity. doi:10.1038/s41366-018-0246-3

Questions

1a. Identify the method used and outline two characteristics of the method.

The study was a quasi-experiment. Although each group was exposed to two conditions, the participants were allocated to either the low BMI or the overweight/obese group.  A quasi-experiment does not have a random allocation of participants, so participant variability may play a role in the findings. In addition, quasi-experiments do not establish a cause and effect relationship because an IV is not manipulated.

1b. Describe the sampling method used in the study.

The sample was a self-selected sample.  This means that the participants were recruited through posters and mailings.  The participants volunteered for this study - meaning that they were willing to take part, although they were deceived as to the actual aim of the study.

1c. Suggest an alternative or additional research method giving one reason for your choice.

Alternative methods could include a survey, structured interview or lab observation.  A survey could ask specific questions regarding how often one thinks about food.  This could help to draw a correlation between the amount of time one thinks about food and one's BMI.  This would allow for a larger sample size and more data for analysis.  Structured interviews could also be used, allowing for a more naturalistic way to gather data and a way to clarify anything that may not be understood by the interviewee - something that is not really possible during a survey.  A lab observation could expose individuals to food and non-food items to see how the participants interact. This is more naturalistic than the computerized model used by Kaiser et al and may have higher ecological validity.

2. Describe the ethical considerations that were applied in the study and explain if further ethical considerations could be applied.

Informed consent would have to be obtained from all of the participants.  The participants are aware that they are in a study and have willingly volunteered, but they have been deceived.  Deception was used in order to avoid demand characteristics, for example, trying harder or a "screw you effect" which may have influenced the findings. In addition, participants would have to be made aware of their rights.  One right is the right to withdraw.  This means that they have the right to leave the study at any time.  For example, when they were asked to come back a year later, they could refuse to do so and have their data withdrawn from the study.  If several participants with a specific trait (eg. low socioeconomic status) drop out of the study, this may lead to a sampling bias and the researcher should report this. Anonymity is also important.  The identities of the participants must be protected; their names should not be revealed and there should be no visual representations that allow for them to be identified.  There is little chance of undue stress or harm in this study, except that one may feel embarrassed when assigned to the "obese" group. It is important that the researcher be supportive of the participants and treat them with respect.  Finally, in the debriefing the deception must be explained and they should be reminded of their rights.  The debriefing should also explain the findings and the implications for the participants - as well as potentially give them advice with regard to the findings.

3. Discuss how a researcher could ensure that the results of the study are credible.

Credibility in quantitative research looks at the validity of the research.  We can look both at internal validity and external validity of the study. 

The study has high internal validity.  The researcher is able to manipulate the "food mindset" and the "non-food mindset" during the experiment, as well as the use of the distractor. The operationalization of the variables is well defined and reasonable.  However, it is not clear from the above study how they "switched" mind-sets and whether the researcher could determine that the appropriate mind-set was applied.  The year period, however, between the original study and the follow up no longer maintains that high level of internal validity as there was no way to control what would happen to the individual over that year period or to measure the level of attentional bias towards food over that time period.

This is linked to the question of external validity. The task was highly artificial - looking at food on the computer.  The food triggers were solely visual - lacking the smells of food which may also act as a distractor. In addition, it was a "one off" experiment, meaning that there was not study of the individual over time. There is a concern that individuals may have been in different "states" in the study - that is, some may have been more hungry than others and some may be more likely to have a "sweet tooth" or other dietary trait. However, the results of the follow-up study seem to affirm that there is ecological validity to the study in that the findings of the quasi-experiment in the lab appear to be supported the study's findings.

Finally, there is the question of population validity. It is questionable whether the sample is a fair representation of the general population as the sample size was relatively small and the participants were all volunteers. One control from the problem of volunteers was that they were not informed of the actual aim of the study. This deception may have helped to increase both the internal validity and the external validity of the study.