PMC

Complexity is defined as “a scientific theory which asserts that some systems display behavioral phenomena that are completely inexplicable by any conventional analysis of the systems' constituent parts.” Reducing a complex system to its component parts amounts to “irretrievable loss of what makes it a system.” Those of us who have decomposed interventions into components for process evaluation might feel uncomfortable at this point. Yes, we may have been able to describe an intervention, say, simply in terms of the percentage of general practitioners who attend the training workshops and the percentage of patients who report having read the leaflets. Thinking about process evaluation in this way is the norm. But by doing so, have we really captured the essence of the intervention? We have, if all we think our intervention to be is the sum of the parts. But that is not, by definition, a complex intervention. It remains a simple one.