Determining overall risk

The risk journal literature lacks a clear and simple account of the conceptual issues involved in determining the overall risk of an action, and in explaining how risk is additive. This article attempts to bring a measure of clarity to these issues in as basic and non-technical a way as possible. First of all, the view that risk is ‘expected harm’ is explained. The view that risk is a quantitative concept is then defended. The distinction between the risk run by doing action A in respect of possible outcome x, and the overall risk run by doing action A in general is explained, as is the position that the overall risk of A is determined by summing the risks of each possible harm that A could give rise to. The article then explains how risks can be summed over time, as long as the probabilities involved are determined according to probability theory. Finally, the article explains that in doing a risk–benefit analysis of A, positive aspects of a possible outcome x, where x is harmful on balance, must be incorporated into x's level of harm rather than incorporated into the benefit side of the risk–benefit analysis of A.