Complexity theory as an approach to explanation in healthcare: a critical discussion.

The reception of complexity theory in health care is characterised by a tendency to reify the idea of a complex system, which is basically an abstraction. This paper argues for three principal theses: first, to invoke complexity, to refer to complex systems, is to proffer a form of explanation; second, in the context of the social sciences, the form of explanation that complexity represents belongs to a family of explanations which the recent theoretical literature associates with social mechanisms; and, third, complexity explanations refer to a specific type of social mechanism, whose features differentiate it from the other members of the family. The most significant of these features is the jettisoning of the default link between order and design, which is precisely the principle omitted by an influential series of papers in the BMJ. Having defended these claims, the paper presents a brief case study illustrating the analysis.