Risk factors, correlation and causation
Something that increases the likelihood of developing a disease is called a risk factor. For example, smoking is a risk factor for lung cancer.
Some diseases, their effects and their risk factors are shown in the table below.
| Risk factor | Disease | Effects |
| Obesity | Type 2 diabetes | The body's cells no longer respond to insulin; blood glucose levels cannot be regulated properly |
| Alcohol | Cirrhosis | Scar tissue is formed in the liver; the liver is unable to remove toxins |
| Smoking | Lung cancer | Carcinogens in cigarette smoke cause cells to become cancerous |
| Risk factor | Obesity |
|---|---|
| Disease | Type 2 diabetes |
| Effects | The body's cells no longer respond to insulin; blood glucose levels cannot be regulated properly |
| Risk factor | Alcohol |
|---|---|
| Disease | Cirrhosis |
| Effects | Scar tissue is formed in the liver; the liver is unable to remove toxins |
| Risk factor | Smoking |
|---|---|
| Disease | Lung cancer |
| Effects | Carcinogens in cigarette smoke cause cells to become cancerous |
Correlation
Scientists look for patterns in data. These patterns can identify risk factors involved in non-communicable diseases.
For instance, data collected have shown links between developing cancer and:
- various How people choose to live. factors
- chemicals produced in the human body or that enter the body
- chemicals in the environment
Below is an example of how a risk factor has been found. This has come from studies on smoking cigarettes and lung cancer.
Historically, in the USA, a pattern can be seen in the amount of cigarette use and the incidence of lung cancer.
As the number of cigarettes smoked has increased over the years, the incidence of lung cancer has increased also. Note that there is a time lag - cancer usually takes some years to develop.
There is a clear association, called a A relationship between two sets of data, such that when one set changes you would expect the other set to change as well., between the variables.
With cancer and other non-communicable diseases, scientists have found many correlations.
Correlation and cause
If there is a correlation between a particular factor and an outcome, it does not mean that the factor necessarily causes the outcome. Scientists must look for a possible mechanism by which the factor could be the likely cause.
In the case of lung cancer, analyses of cigarette smoke have shown that at least 70 of the chemicals present in smoke will cause cancer in laboratory animals which establishes a causal link.
