Many environmentalists might well argue that principles are only principles, and process is only process; policy outcomes (that is, the influence of any EPI related activity on the state of the environment) are what really matter. However, the measurement of outcome effectiveness is a very difficult task, and one that is not helped by the relative immaturity of this particular sub-field of evaluation research. In the case of EPI, the main ‘subject’ – that is, the state of the environment now and in the long run – is a highly complex matter, affected by a multitude of factors. Good data is hard to come by. Moreover, there are many different instruments that have been applied to deliver EPI as well as background factors such as economic and technological development, basic features of democracy (for example, veto points, democratic style), the prevailing regulatory culture and levels of public opinion. From an analytical perspective, the existence of so many potential causal factors and implementing instruments implies that causality cannot easily be determined, despite many confident claims that integration is (or is not) working.