Variation in the operationalisation of dose in implementation of health promotion interventions: insights and recommendations from a scoping review

BACKGROUND: While ‘dose’ is broadly understood as the ‘amount’ of an intervention, there is considerable variation in how this concept is defined. How we conceptualise, and subsequently measure, the dose of interventions has important implications for understanding how interventions produce their effects and are subsequently resourced and scaled up. This paper aims to explore the degree to which dose is currently understood as a distinct and well-defined implementation concept outside of clinical settings. METHODS: We searched four databases (MEDLINE, PsycINFO, EBM Reviews and Global Health) to identify original research articles published between 2000 and 2015 on health promotion interventions that contained the word ‘dose’ or ‘dosage’ in the title, abstract or keywords. We identified 130 articles meeting inclusion criteria and extracted data on how dose/dosage was defined and operationalised, which we then synthesised to reveal key themes in the use of this concept across health promotion interventions. RESULTS: Dose was defined in a variety of ways, including in relation to the amount of intervention delivered and/or received, the level of participation in the intervention and, in some instances, the quality of intervention delivery. We also observed some conflation of concepts that are traditionally kept separate (such as fidelity) either as slippage or as part of composite measures (such as ‘intervention dose’). DISCUSSION: Dose is not a well-defined or consistently applied concept in evaluations of health promotion interventions. While current approaches to conceptualisation and measurement of dose are suitable for interventions in organisational settings, they are less well suited to policies delivered at a population level. Dose often accompanies a traditional monotonic linear view of causality (e.g. dose response) which may or may not fully represent the intervention’s theory of how change is brought about. Finally, we found dose and dosage to be used interchangeably. We recommend a distinction between these terms, with ‘dosage’ having the advantage of capturing change to amount ‘dispensed’ over time (in response to effects achieved). Dosage therefore acknowledges the inevitable dynamic and complexity of implementation. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s13012-019-0899-x) contains supplementary material, which is available to authorized users.