Defining and explaining risk
In Chapter 1 we described risk as 'the probability that something unpleasant will happen' (following the definition put forward by the British Medical Association in 1990). In this chapter we expand on this definition and on the different uses of the term, and show how its meaning has changed over time. We also look at different theoretical models of r isk, as well as at issues that ar ise in the assessment, perception and management of risk, and how these relate to the problem of how to communicate information about risk effectively.
One of the most frequently quoted definitions of risk, particularly in relation to health and safety, is that set down by the Royal Society Study Group in 1983. They defined risk as the 'probability that a particular adverse event occurs during a stated period of time, or results from a particular challenge. As a probability in the sense of statistical theory, risk obeys all the formal laws of combining probabilities' (Adams 1995: 8). The Study Group distinguished between the risk itself and the 'harm' experienced as a result of an adverse event. In doing so, they defined 'detriment' as 'a numerical measure of the expected harm or loss associated with an adverse event… It is generally the integrated product of risk and harm and is often expressed in terms such as costs in pounds, loss in expected years of life or loss of productivity, and is needed for numerical exercises such as cost-benefit analysis or risk-benefit analysis' (Adams 1995: 8). Thus, these are very 'objective' definitions that allow little room for the role of subjective perceptions and experiences. We will see shortly that not everyone interprets and uses the term 'risk' in this way.
Usage of the term 'risk' varies, or is at least given different types of emphasis in different scientific disciplines. In epidemiology, for example,