What types of interventions reduce or worsen inequalities in adolescent smoking? A review of the literature and reanalysis of intervention studies.

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In many developed countries including the UK, health outcomes improve significantly as socioeconomic position (SEP) increases. Poorer health behaviours among lower SEP individuals contribute to these inequalities. In particular, while smoking rates have fallen in recent times, smoking remains more common among lower SEP individuals. Most smoking uptake occurs in adolescence (1 in 9 English adolescents are daily smokers by age 15), with socioeconomic inequalities emerging in adolescence before tracking into adulthood. Hence, action to reduce inequalities in adolescent smoking may play a vital role in reducing inequality. There is increasing debate regarding what types of actions might increase or decrease health inequalities. Many argue from perspectives such as socio-ecological theory or the theory of fundamental causes, that interventions based upon education or individual choice may widen inequality, while targeting more structural factors, such as pricing and availability may reduce inequality. However, there is currently limited empirical evidence for these propositions, as few studies have analysed effects by SEP, or attempted to identify what types of actions reduce or increase existing inequalities, in what contexts. The study will involve a review of current published evidence for impacts of such intervention on inequalities and reanalysis of published studies which collected measures of SEP. Phase 1 will be largely descriptive and will aim to examine the extent to which socioeconomic inequalities have been considered in the design of evaluations and interventions to reduce adolescent smoking. Systematic searches of a range of databases will be used to identify intervention studies in developed countries since the turn of the century. How commonly, and in what ways, differential effectiveness was examined (e.g whether via subgroup analysis, use of interaction terms, or targeting of interventions toward lower SEP groups) within such studies will be examined. How commonly, and in what ways, impacts on inequalities in adolescent smoking are considered in intervention development will also be examined. The extent and nature of consideration of impacts on inequality in intervention and evaluation design will be compared across intervention types (i.e individual level, community level, or society level intervention). Harvest plot methodology will be used to combine studies which examine impacts of different levels of intervention on socioeconomic inequality. A database of studies which collected measures of SEP will be compiled, with studies labelled according to intervention type, study quality and country. Studies to be reanalysised in Phase 2 will be sampled from this database. Phase 2 will aim to advance our understandings of the impacts of various types of public health interventions upon socioeconomic inequalities through reanalysis of datasets from intervention studies which collected measures of SEP. Up to 40 studies will be selected from the database developed during Phase 1, representing a range of i) individual, ii) community, iii) society and iv) multi-level interventions from a range of developed countries. Corresponding authors will be contacted by email and asked whether any unpublished analyses of differential effectiveness were conducted, and if so, if they are willing to share these. Where they were not, authors will be asked to supply original data, which will be reanalysed for differential effectiveness by SEP, or to conduct reanalysis and supply syntax and log files. The harvest plot will then be extended to incorporate these additional analyses, with effects combined using meta-analysis where feasible. The study will provide policymakers with information on how their actions might impact inequalities, advance social science theory for reducing inequalities, and highlight the importance of designing evaluations in a manner which captures impacts on inequality.