Risk factors and their identification. First Part: What is a risk factor?

This series of three articles reviews the designs of studies which can be used to identify risk factors of a disease, here: diabetes or complications of diabetes. In the present issue of Diabete & Metabolisme, the first article of the series, we give the definition of a risk factor, along with measures of its force--relative risk and odds ratio, followed by the epidemiological definitions of the diseases: diabetes, coronary heart disease and hypertension. Risk factors are further discussed and we complete the discussion by some observations on the bias which can arise from a study or from its analysis, which can lead the researcher to the wrong conclusion. The three types of epidemiological studies which are used to determine whether factors are associated with a disease: observational or cross-sectional studies, cohort studies and case-cohort studies will be described in the second of the series in the next issue of the journal. Examples will be provided of each of these study types; their advantages and disadvantages will be discussed. In a third issue, the final paper will provide some examples of the study types and the identification of risk factors. The first examples involve diabetes and pancreatic cancer, the second birth weight and non-insulin dependent diabetes. Having found an association between a risk factor and diabetes, then we will discuss whether it can be considered to be a risk factor and if so and whether it is likely to be a cause of the disease.