There is growing evidence that a diet high in processed foods increases the risk of various diseases. To explore whether the risk of depression may be increased by a diet high in processed foods, researchersrecruited a total of 379 young adults with a new diagnosis of depression and 344 young adults without depression. The study participants were questioned about processed food intake over the preceding year. The table below presents the study findings:

		Depression
		Yes	No
High processed food intake	Yes	54	32
No	325	312
		379	344

1. What is the appropriate measure of association for this study? (1 mark)

Answer here: The appropriate measure of association for this case-control study is the odds ratio because the study is comparing the odds of depression among individuals with high processed food intake to the odds of depression among individuals without high processed food intake. This measure is used in case-control studies and is suitable for estimating the strength of the association between an exposure and an outcome.

1. Please calculate this measure. (2 marks)

To calculate odds ratio, we use the following formula: -

OR = odds of exposure in cases =a/c

Odds of exposure in controls =b/d

OR= a*d/ b*c = 54*312/32*325

OR = 16,848/10,400

OR = 1.62

So, the odds ratio is approximately 1.62. This means that the odds of having depression among individuals with a high processed food intake are 1.62 times the odds of having depression among individuals without a high processed food intake.

1. Please interpret the result. (2 marks)

The odds of having a high processed food intake are 1.62 times higher among young adults with a new diagnosis of depression compared to young adults without depression. This suggests a possible association between high processed food intake and the risk of developing depression.

1. A reviewer of the study suggested that socio-economic status has the potential to cause confounding in this situation. Use the conditions/criteria for confounding covered in this unit to explain how this could occur. Suggest one method to address confounding in data analysis. Answer using complete sentences. (3 marks)

Socio-economic status could be a confounder in this study if it is associated with both the exposure (processed food intake) and the outcome (depression), and it is not an intermediate step in the causal pathway between the two. For example, individuals with lower socio-economic status might have a higher likelihood of consuming processed foods due to cost and accessibility, and they might also have a higher risk of depression due to stressors associated with lower socio-economic status.

To address confounding in data analysis, one method would be to stratify the analysis by socio-economic status or to include it as a covariate in a multivariable logistic regression model.

1. Name a type of measurement bias/error that would be of particular concern in this type of study and in this specific scenario. (2 marks)

A type of measurement bias/error of particular concern in this type of study is recall bias.

This occurs when study participants do not accurately remember past events or exposures.

In this scenario, individuals with depression might recall their food intake differently than those without depression, either by underreporting or overreporting their consumption of processed foods.

This could lead to differential misclassification of the exposure status and affect the validity of the study's findings.