What does research involve?

Researchers, to be specific epidemiologists, attempt to determine what factors are associated with diseases (risk factors), and what factors may protect people or animals against disease (protective factors). The science of epidemiology was first developed to discover and understand possible causes of contagious diseases like smallpox, typhoid and polio among humans. It has expanded to include the study of factors associated with non-transmissible diseases like cancer. These studies can only show evidence that a particular risk factor is associated with a higher incidence of disease in the population exposed to that risk factor. This is why you have read the word "association" a lot in the previous sections.

In order to prove that a particular risk factor is the factor "causing" the disease, laboratory studies need to be carried out.

The strength of a study depends on the number of cases and control included in the study. The more individual cases that are included in the study, the more likely it is that a significant association will be found between the disease and a risk factor.

When is an external factor considered a "risk factor"?

Finding a risk factor for a disease is an intensive work that comprises gathering data, generating a broad range of biomedical and psychosocial theories or expand theories, testing hypotheses and finally making educated, informed assertions about which relationships are causal and about how they are causal.

The below hierarchy shows typical studies starting from generating a hypothesis to establishing causality.

GENERATE HYPOTHESIS - Case reports -> Case series -> Ecological studies -> Cross-sectional studies -> Case-control studies -> Cohort studies -> Randomized controlled trials - ESTABLISH CAUSALITY

Some of these steps like the cohort studies can take years to conduct.