Statistical measurements of the state of the natural environment and of environmental damage are at a somewhat experimental stage. For some environmental elements that are, in principle, subject to measurement - such as the physical conditions of air, water and soil - there is considerable uncertainty among scientists about what it is most important to measure. There is a need to apply statistical techniques both to monitoring procedures and to assessing the costs and benefits of policy actions already taken or under consideration (the benefits being generally more diffuse and difficult to quantify than the costs); and to integrate the statistics with socio-economic data.