6 Causal Thinking in Epidemiology
Sheena Martenies
Causal Thinking in Epidemiology
Overview
As we covered in previous chapters, an important function of the field of epidemiology is documenting the frequency, distribution, and patterns of health and disease within a population. Another important goal of the field of epidemiology is identifying the factors that cause health and disease to occur within a population. Determining whether a health behavior, environmental exposure, or dietary component, for example, is the cause of a health or disease state is necessary for identifying strategies to promote health in a population. When epidemiologists and public health practitioners identify causal factors, they can better spend time and resources in ways that will have an impact on population health.
Sometimes identifying causal factors is as simple as identifying the source of a foodborne illness outbreak or the gene mutation that results in a disease. Other times, identifying causal factors requires epidemiologists to assess several different types of evidence before drawing conclusions about a risk factor under investigation. In this chapter, we’ll discuss how epidemiologists think about causality and the steps they work through when identifying the causes of health and disease states.
Learning Objectives
By the end of this chapter, you will be able to:
- Discuss why identifying causal factors is important for epidemiology and public health practice
- Explain the difference between correlation and causation
- Describe the criteria by which epidemiologists determine if a specific factor is a cause of a disease
What is Causality?
Causality is the idea that outcomes are attributable to events that came before them. That is, if event A occurs, outcome B will occur as a result. In epidemiology, we are interested in understanding the causes of health and disease states. This involves identifying the factors that come before disease—called risk factors—or the factors that result in good health.
Causes of health or disease are diverse. For some diseases, there is an important genetic cause. For example, cystic fibrosis is a disease caused by a mutation in the gene for the protein that moves salt in and out of cells. Individuals who inherit two copies of the mutation for this gene will develop cystic fibrosis.[1] This mutation is a genetic risk factor for the disease. Other diseases have strong behavioral or environmental risk factors. A classic example is lung cancer. Lung cancer can be caused by behavioral (smoking) or environmental (radon, diesel exhaust) factors.[2]
In reality, most diseases are caused by complex interactions between genetic factors and behavioral or environmental factors. For example, people with a family history of heart disease who also smoke or drink alcohol may be at the highest risk for coronary heart disease compared to people with other risk factor profiles.[3] This combination of risk factors (genetic, behavioral, and environme