Introduction

Any concern with an intervention's resource inputs, effectiveness and performance (outputs) is likely to need at least some consideration of how they came about. This goes well beyond what might typically be done through monitoring activities and engagement, and calls for a more rounded assessment if decision- makers are to draw sensible conclusions about what has resulted against their expectations. As the title implies, this focus on intervention mechanisms, their effective working and performance is the bedrock of process evaluation.

To be purposeful, process evaluations go deeper than results to probe interplay between individual and organisational dynamics for an intervention. The nucleus will always be with assessing how an intervention has worked against expectations (or targets), both overall and for specific constituent parts of it. Those dynamics, and the intervention aspirations and mechanisms which fuel them, are the prism through which the evaluation disentangles how, and how well, the intervention has or is working – its underpinning processes.

What ‘processes’, why and when to evaluate them

Process evaluations are a long- established, and still important, part of the evaluator's armoury. They can be stand- alone inquiries or may involve pluralistic approaches (Chapter 5) within an impact- focused or theory- based evaluation. For simplicity, this chapter looks at process evaluation as a distinct approach, but the principles and practice set out can be applied equally when combined with, or as an embedded part of, another type of evaluation.

The domain of a process evaluation can be wide but has some limitations. Figure 6.1 sets out the essential sequential parts that characterise any intervention; process evaluation is concerned with only the first parts of this sequence.