In the early years of envirnmental assessment, a relatively simple schema was used to help structure assessments and identify indicators - the so-called PSR (Pressure-State-Response) model, initially developed on behalf of the OECD.  In time, the limitations of this became apparent, and a number of initiatives were started to devise something more appropriate.  Out of these emerged the DPSIR framework, which was taken up and applied as a basis for assessment by the European Environment Agency.

As the diagram to the left indicates, this sees environmental impacts as originating in driving forces (D) such as industrial activity or transport, which lead to pressures on the environment (P) through emissions, land take etc, and thereby change the state of the environment (S) in different ways.  These changes lead to a range of impacts (I), both on the environment and on human society (including health effects).  Policy and other responses (R) are taken to control these impacts, targetted at different points in the causal chain.  Notably, in the case of the environment, preventative measures (targetted at the sources) tend to be most effective, because these can avoid environmental damage.  Later intervention, after damage has been caused, tends to be much less effective, because of ther cost and difficulty of cleaning up pollution, or repairing other forms of damage, once they have occurred.