Pragmatic trials of complex psychosocial interventions: methodological challenges

Having first introduced the pragmatic health care trial, the discussion then focuses on a selected list of technical problems that are important for the design, analysis and inference from such trials. The first is lack of independence of participants' outcomes do to clustering either arising from a cluster randomized design or to the way treatment is delivered (therapist and group effects). The second and third concern the implications of non-adherence to treatment and subsequent loss to follow-up, particularly, when non-adherence is associated with missing outcome data. Finally, it is argued that pragmatism and a desire for a scientific explanation should not be regarded as mutually exclusive.