Risk matrices: implied accuracy and false assumptions

Risk matrices are used during hazard identification and risk assessment processes and provide a construct for people needing to display the two variable relationship between likelihood and consequence that are considered to be the elements of risk. The purpose of a matrix is to reduce the continuum of risk into ranges or bands such as high, medium or low. These bands are often allocated colours such as red for the highest risks to green for the lowest. Sometimes each band in a matrix is allocated a numerical value or range. The multiplication of likelihood and consequence implies a quantitative basis although it may not be widely understood. The multiplication operator produces lines of equal risk that a matrix cannot model accurately and thereby introduces risk reversal errors. Weaknesses in matrices are further compounded by subjectivity and bias introduced by users and the value of such tools is brought into doubt. A shift of emphasis from the risk assessment stage to the risk control stage of a hazard management process may lead to better and more timely decision making and better use of resources.C