Question

Epidemiology: Draw a DAG of the relationship between exposure and outcome, accounting for other variables discussed. Then, write either “Yes” if it appears that confounding of the relationship between the exposure and the outcome is supported (based on the general rule for confounding) and “No” if it appears that confounding is not supported. If “No”, please indicate why it is not a confounder.

• Researchers are investigating a potential association between high-density lipoprotein (HDL) cholesterol and lung cancer where there appears to be a relationship between low HDL and lung cancer. Smoking is known to cause a decrease in HDL levels and is known to cause lung cancer.

Answer 1

Statement: Researchers are investigating a potential association between high-density lipoprotein (HDL) cholesterol and lung cancer where there appears to be a relationship between low HDL and lung cancer. Smoking is known to cause a decrease in HDL levels and is known to cause lung cancer.

Epidemiology: Draw a DAG of the relationship between exposure and outcome, accounting for other variables discussed. Then, write either “Yes” if it appears that confounding of the relationship between the exposure and the outcome is supported (based on the general rule for confounding) and “No” if it appears that confounding is not supported. If “No”, please indicate why it is not a confounder.

Answer:

Terminology

DAG: Directed acyclic graph (finite directed graph having no directed cycles)

Confounding: It refers to the risk factor to which the population is exposed. In this case, the risk factor is smoking. Hence, based on the general rule for confounding the comparison can be done between two populations (i) healthy population unaffected by smokiking and the other (ii) Population affected by external risk factor (smoking).

Desription

1. There is a reciprocal relationship between high-density lipoprotein (HDL) cholesterol and lung cancer. It means if the HDL will be high there will be low probability of having lung cancer. It can be understand that the healthy poplation having high HDL level are less prone to lung cancer.
2. If we consider about the population who smoke or affected by smoking, their low-density lipoprotein (LDL) will be high than HDL and becomes very prone to or susceptible to lung cancer.

The Directed acyclic graph for the current study is as follows:

Figure 1. Directed acyclic graph for two population healthy and exposed to risk factors and their association to the lung cancer.

Abbreviations: + indicates increse and - indicates decrease