Walking the talk on multi-level interventions: The power of parsimony.

There is strong consensus regarding the need for multi-level interventions (MLIs) to address today's complex health problems. Several longstanding social ecological frameworks are commonly referred to in guiding MLI development. The specificity and comprehensiveness of these frameworks unwittingly suggest that the totality of included influences are important in all health contexts. Not surprisingly, when viewed as requiring intervention at all levels of influence, MLIs are often considered to be infeasible due to sizeable cost and logistical barriers. Thus, efforts to develop and evaluate MLIs have been extremely limited, and comparatively few examples are found in the health literature. We argue that operational frameworks to identify which levels matter in which contexts - henceforth, referred to as parsimony - could accelerate the field towards broader use of MLIs. We suggest a hypothetical operational framework informed by complexity theory and pragmatic approaches that could enable us to conceptualize, design and evaluate MLIs to consider where reflexive and recursive process mechanisms that cross levels should be targeted by MLI. The approach also emphasizes sustainability of MLIs. Without developing parsimony-based operational frameworks to move us forward, we fear that little will change, and we will simply continue to talk, without proceeding to the walk.