Last updated: 6-Jul-2011
Appendix A: Reviews Used in this Section
One influential service for researchers, clinicians, health planners, and policy-makers is the Cochrane Database of Systematic Reviews (CDSR or Cochrane). In 1979, the British epidemiologist Archie Cochrane[1] called for “a critical summary, adapted periodically, of all…relevant randomized controlled trials.”[2] By the early 1990s many practitioners and consumers had fully realized the importance of systematic reviews, in an easily accessible form, for making decisions in healthcare.
Systematic reviews are prepared and maintained by the Cochrane Collaboration in The Cochrane Library, along with quality-assessed material on the effects of healthcare interventions submitted by others. The Cochrane Collaboration, made up of various Review Groups, remains a loose-knit organization. Nevertheless, their reports, which are regularly updated as more information becomes available, “are now widely regarded as being of better quality, on average, than their counterparts in print journals.”[3] The CDSR was regularly accessed as an evidence base for the interventions reviewed in this report. This was especially useful when large volumes of studies are available focusing on specific interventions, as is the case for interventions to reduce consumption of and exposure to tobacco.
In this report we accessed many reviews prepared by groups other than the CDSR. For example, the Canadian Task Force on Preventive Health Care (formerly the Canadian Task Force on the Periodic Health Examination) will inform the discussion, as well as a key report from the Canadian Population Health Initiative. Also useful were the assessment programs which exist in the UK (e.g., Health Technology Assessment / National Institute of Clinical Excellence) and in the US (e.g., Surgeon General reports, Task Force on Community Preventive Services or TFCPS, etc.).
The TFCPS bears more comment as it may not be as well known as CDSR, though it has already produced influential evidence reviews for smoking, physical inactivity, and exposure to ultraviolet light, with work on nutrition currently in process. This independent non-federal Task Force makes recommendations for population health programs and policies based on scientific evidence about what practices have worked to improve health. Its main output is the Guide to Community Preventive Services (Community Guide), which summarizes the scientific literature on a specific topic, evaluates their quality according to established criteria, and makes evidence-based recommendations according to an intervention’s proven effectiveness. The continuously updated results have been published on the internet and in various publications since 1999.[4]
Cochrane and equivalent systematic reviews tend to focus mainly on randomized controlled trials (RCTs). Well-designed and implemented RCTs are considered the "gold standard" for evaluating an intervention's effectiveness. In the absence of RCTs, however, other methodologically sound studies are sought regarding the effectiveness of an intervention.[5] For example, in a recent CDSR review[6] the “authors recognise the possibility of not finding such a design (RCT) for general population prevention studies; therefore the review will include data from ‘controlled before-and-after studies’ and ‘interrupted time series’.”
Another potential source of information is general practice guidelines. These are useful as they often attempt to pull together data on a number of interventions; however, such reviews are usually not as up-to-date as CDSR and sometimes lack rigor in ensuring that all claims are linked to evidence.
In addition to accessing review programs and articles, this report will scan the published and ‘grey’ literature[7] to identify any more recent studies that are of sufficient quality methodologically to include in the summary of interventions.
[1] Hill GB. Archie Cochrane and his legacy. An internal challenge to physicians' autonomy? Journal of Clinical Epidemiology 2000; 53(12): 1189-92.
[2] Source: http://www.updatesoftware.com/history/clibhist.htm#Dickersin_etal1998 (accessed October 2004).
[3] Jadad AR, Cook DJ, Jones A et al. Methodology and reports of systematic reviews and meta-analyses: a comparison of Cochrane reviews with articles published in paper-based journals Journal of the American Medical Association 1998; 280: 278-80. Other review articles are often highly dependent on Cochrane summaries.
[4] Briss PA, Brownson RC, Fielding JE et al. Developing and using the Guide to Community Preventive Services: lessons learned about evidence-based public health Annual Review of Public Health 2004; 25: 281-302.
[5] Stroup DF, Berlin JA, Morton SC et al. Meta-analysis of observational studies in epidemiology: a proposal for reporting Journal of the American Medical Association 2000; 283(15): 2008-12.
[6] Gimenez-Perez G, Gonzalez-Clemente JM and Aauricio D. Lifestyle interventions for preventing type 2 diabetes mellitus (protocol). Cochrane Tobacco Addiction Group Cochrane Database of Systematic Reviews. 3, 2004. The authors define a controlled before-and-after study “as a design where there is contemporaneous data collection before and after the intervention and an appropriate control site or activity”. An interrupted time series is defined as “a design where there is a clearly defined point in time when the intervention occurred and at least three data points before and three after the intervention”.
[7] “Grey literature refers to publications issued by government, academia, business, and industry, in both print and electronic formats, but not controlled by commercial publishing interests, and where publishing is not the primary business activity of the organization. Scientific grey literature comprises newsletters, reports, working papers, theses, government documents, bulletins, fact sheets, conference proceedings and other publications distributed free, available by subscription, or for sale.” Weintraub I. The Role of Grey Literature in the Sciences. Available at http://library.brooklyn.cuny.edu/access/ greyliter.htm (accessed November 2004).