1.3 An alternative perspective on causality
I would estimate fairly confidently that most of you will be familiar with a linear or successionist explanation of causality. Put simply it boils down to: ‘we did x and y happened, therefore x is responsible for y’. This is a straightforward input–output approach to evaluation. An evaluator working to this paradigm will typically make causal inferences on the basis of data that appears to reveal regularities in the patterning and occurrence of events. In addition, it is assumed that the identification of regularities means it is possible to generalise the results from one context to another. For example, biometric readers installed at airports A and B slowed down passenger throughput by 5 per cent therefore we can expect the same results at airports C, D, E and so on.
This approach to causality, and the evaluations that incorporate it, is frequently challenged, but is nevertheless popular. In many fields of evaluation it can be regarded as the dominant or conventional paradigm (Clarke, 1999; Weiss, 1998).
The example that follows, which is drawn from my own experience, details how a successionist approach to evaluation was employed. It centres on the installation of CCTV (closed circuit television) in certain towns and cities in the UK in the mid-1990s (for a fuller discussion see Beck and Willis, 1995).