Calculation, expression and perception of risk in medicine: implications for clinical decision-making.

: In medicine, risk is usually related to a factor (known as a risk factor) that (often in conjunction with other risk factors) modulates the probability of a disease or event occurring, worsening or improving in individuals in whom it is present. Clinicians are faced on a daily basis with decisions on risk that--for example in therapeutics--involve calculation of the benefit-risk balance. Individuals (whether or not they are ill) are also confronted with risk in their decision-making. In this paper we discuss the clinical uses of the concept of risk, the main types of study that define and measure it, and the main types of bias most commonly associated with the perception and interpretation of risk in medical decision-making.