An aspect of a person’s condition, lifestyle or environment that affects the chance of them getting a disease. For example, cigarette smoking is a A way of expressing the chance of an event taking place, expressed as the number of events divided by the total number of observations or people. It can be stated as ‘the chance of falling were one in four’ (1/4 = 25%). This measure is good no matter the incidence of events i.e. common or infrequent. factor for lung cancer.