The Canadian Task Force on Preventive Health Care is an independent panel of clinicians and methodologists with expertise in prevention, primary care, literature synthesis, critical appraisal and the application of evidence to practice and policy. The task force makes recommendations about clinical manoeuvres aimed at primary and secondary prevention. (Please see www.canadiantaskforce.ca/members_eng.html
for a list of current members of the task force.)
Work on each recommendation is led by a workgroup of two to five members of the task force; a list of members of the workgroup for the current guidelines is available at the end of this article. Each workgroup establishes the research questions and analytical framework for the guideline.
The Evidence Review and Synthesis Centre (the details of which are available at www.canadiantaskforce.ca/about_eng.html
) assembles a team of methodologists who will perform the systematic review, usually in conjunction with one or more clinical experts. The team provides input on the analytical framework, then summarizes the evidence using a systematic review and quantitative summary of the relevant available evidence; narrative summaries are developed when quantitative synthesis is not feasible. A list of members of the evidence review team for the current guidelines is available at the end of this article.
Once the systematic review is available from the evidence review team, the task force workgroup independently develops the recommendation statements by consensus, based on a detailed review of the evidence. In formulating recommendations, workgroups consider both the benefits and harms associated with a screening test, patient values and preferences, the quality of the evidence and, in some cases, the costs of the intervention (Box 1
). The strength of evidence is determined using the Grades of Recommendation Assessment, Development and Evaluation (GRADE) system.10
The draft recommendations as developed by the workgroup are revised and approved by the entire task force.
Box 1: Grading of recommendations
- Recommendations are graded as either strong or weak according to the Grades of Recommendation Assessment, Development and Evaluation system (GRADE).10 GRADE offers two strengths of recommendation: strong and weak. The strength of recommendations is based on the quality of supporting evidence, the degree of uncertainty about the balance between desirable and undesirable effects, the degree of uncertainty or variability in values and preferences, and the degree of uncertainty about whether the intervention represents a wise use of resources.
- Strong recommendations are those for which the task force is confident that the desirable effects of an intervention outweigh its undesirable effects (strong recommendation for an intervention) or that the undesirable effects of an intervention outweigh its desirable effects (strong recommendation against an intervention). A strong recommendation implies that most people will be best served by the recommended course of action.
- Weak recommendations are those for which the desirable effects probably outweigh the undesirable effects (weak recommendation for an intervention) or undesirable effects probably outweigh the desirable effects (weak recommendation against an intervention) but appreciable uncertainty exists. A weak recommendation implies that most women would want the recommended course of action, but many would not. For clinicians, this means they must recognize that different choices will be appropriate for individual women, and they must help each woman arrive at a management decision consistent with her own values and preferences. Policy-making will require substantial debate and involvement of various stakeholders. Weak recommendations result when the balance between desirable and undesirable effects is small, the quality of evidence is lower, and there is more variability in the values and preferences of patients.
- Evidence is graded as high, moderate, low or very low based on how likely further research is to change our confidence in the estimate of effect.
Although members of a task force workgroup are not necessarily content experts in the clinical area of the guideline, a content expert is part of the evidence review team, and the research questions, systematic review and recommendations undergo internal and external peer review by experts in the field and by stakeholders and partners, such as the Canadian Breast Cancer Screening Initiative for these guidelines. Details about the task force’s methods can be found elsewhere11
and in Appendix 1 (available at www.cmaj.ca/lookup/suppl/doi:10.1503/cmaj.110334/-/DC1
Key questions and analytic framework for systematic review
The Breast Cancer Workgroup established key questions and an analytic framework for the systematic review on screening for breast cancer (). Key questions were addressed by systematic review. Contextual questions (issues judged not to require a systematic review, but that were addressed by targeted literature searches) are also shown in .
Analytical framework and key questions posed by the workgroup. MRI = magnetic resonance imaging.
Because previous guidelines have emphasized the benefit of mammography for screening women aged 50–69 years, the focus of the review was women aged 40–49 years and women aged 70 years and older; data were collected for women aged 40 years and older. Randomized and quasi-randomized controlled trials were used to determine the effectiveness of screening interventions (, key questions 1a, 1b and 1c). Observational studies and mathematical models were not used to assess efficacy owing to their potential for bias and because there was sufficient trial data to answer the key research questions.
Randomized trials often fail to capture detailed information on clinically relevant harms and generally do not study patient values and preferences. We used observational data to assess these issues (, key questions 2a, 2b and 2c, and contextual questions).
Because a high-quality systematic review from the United States Preventive Services Task Force10
(a national organization with a mandate similar to that of the Canadian Task Force on Preventive Health Care) had recently been published, we chose to update their search to avoid duplication of effort. The previous summary of evidence was used for evidence up to the end of 2008, and an updated search for new evidence published after that time was done by the evidence review team. Because our initial search did not identify sufficient age-specific data to assess the harms of mammography, we did an additional search of data from Canadian organizations including the Public Health Agency of Canada and the Canadian Institute for Health Information. The systematic review upon which the current guidelines are based and an update as of October 2011 are published on the task force’s website.12