Question

Foodborne epidemiologists at the local health department investigated an outbreak of food poisoning at a Cinco de Mayo potluck dinner. Initially the epidemiologists determined that nachos were the cause of the outbreak. However, upon closer review lettuce was determined to be the true cause of the outbreak.

6a. In this example, would you expect lettuce to act as a positive or negative confounder on the relationship between nachos and food poisoning? Explain your answer.

6b. Assume that you want to analyze the association between nachos and food poisoning. Provide a method to control for the confounder lettuce in the design of your study. Please be specific.

Answer 1

Confounding is a situation in which the effect or association between an exposure and outcome is distorted by the presence of another variable. Positive confounding (when the observed association is biased away from the null) and negative confounding (when the observed association is biased toward the null) both occur.

As we know that the term "null hypothesis" is a general statement or default position that there is no relationship between two measured phenomenon.

6a. According to question there are two food items under suspicion. One is nachos which is a dish from northern Mexico and another one is lettuce which is an annual plant of the daisy family, Asteraceae.

According to null, there should not be any relation between food poisoning and lettuce but later on lettuce was found responsible. That means lettuce is going away from null or it is biased away from null. So lettuce is acting as positive confounder.

6b. If we want to estimate the relation between food poisoning and nachos then lettuce will be taken as positive confounder which is clear from the above paragraph. Absence of lettuce must confirm non occurring of poisoning. Absence of lettuce will act as control. Now again frequency of poisoning will be observed alongside the quantification of poisoning outbreak.

Negative results will confirm non relationship between nachos and food poisoning.