Focus on methods key for advancing population health intervention research.

I would like to thank the CJPH for their commitment to population health intervention research (PHIR). Publication of the special issue “Population Health Intervention Research: Advancing the Field” (CJPH, Vol. 103, Supplement 1, September/October 2012) sheds light on elements in need of clarification and debate among population health intervention researchers. Despite a high level of conceptual discussion within the special issue about what is and is not a population health intervention, I am concerned with the limited focus on methods. Dr. Louise Potvin points to the need for defining “what methods are recognized as valid by the community of population health intervention researchers?”1 p.S63 Reading the quantitative studies in the special issue, it is clear that PHIR is lagging behind methodologically compared to other overlapping research areas examining policies or programs operating outside of the health sector, including social epidemiology and economics.2,3 These areas have traditions of applying methods able to control for confounding and of open methodological debate.4,5 In many cases in the special issue, better methods could have been applied to the available data and were not. For example, Cushon et al.6 pooled 2003-2007 data into a preintervention time period and compared this to the post-intervention years (2008-2009) to examine the effect of their vaccination intervention. The authors recognized the need to control moving averages and seasonal effects, but did not do so. Interrupted time series analysis using the available monthly data would have controlled potential confounders and improved the plausibility of the effect estimate.7 The questions posed by population health intervention researchers are important and require evaluation. However, I am concerned that conceptual debate surrounding PHIR will sink into rhetoric and dominate our discussions, while the methods used in quantitative evaluations of population health interventions will languish and be so easily critiqued that the findings will have little influence on policies that can “reduc[e] risk exposure in successive cohorts of people within the setting(s) under investigation.”8, p.I9 Evaluation methods must be at the forefront of discussion and debate if population health intervention research is to flourish as a field.