Note from the National Guideline Clearinghouse (NGC): An evidence review was prepared by the Duke University Evidence-Based Practice Center (EPC) under contract to the Agency for Healthcare Research and Quality (AHRQ) (see the "Availability of Companion Documents" field).
Data Abstraction and Development of Evidence Tables
The Duke research team developed data abstraction forms/evidence table templates for abstracting data for the various key questions (Appendix C in the Evidence Review [see the "Availability of Companion Documents" field]). Based on clinical expertise, a pair of researchers was assigned to the research questions to abstract data from the eligible articles. One of the pair abstracted the data, and the second researcher over-read the article and the accompanying abstraction to check for accuracy and completeness. The completed evidence tables are provided in Appendix D in the Evidence Review (see the "Availability of Companion Documents" field).
Quality Assessment Criteria
At the data abstraction stage, the abstracting researcher was asked to evaluate each included article for methodological quality. For Question 2 regarding analytic validity, EPC staff assessed quality of studies based on questions in the Analytic validity, Clinical validity, Clinical utility and associated Ethical, legal and social implications (ACCE) model for evaluation of genetic testing (Appendix E in the Evidence Review [see the "Availability of Companion Documents" field). For all other questions for which we could identify data, EPC staff intended to use the quality assessment criteria developed by the Tufts-New England Medical Center Evidence-based Practice Center for an evidence report on "Effects of Omega-3 Fatty Acids on Cardiovascular Disease." However, these criteria require the study to be either a randomized controlled trial, longitudinal cohort study, or case-control study, and none of the studies identified for this report had these study designs. Therefore, EPC staff elected to use criteria developed by the Oxford Centre for Evidence-based Medicine (Appendix E in the Evidence Review [see the "Availability of Companion Documents" field) to evaluate individual studies based on type of the study (therapy vs. prognosis vs. prevalence) and strength of study design, with numerical scores ranging between 1 and 5 (including 1a, 1b, 1c, 2a, 2b, 2c, 3a, 3b, 4, 5). The overall strength of recommendation for each question was then graded for each question as A, B, C, or D according to criteria that take into account the quality of individual studies identified for each question. The quality assessment scores for individual studies are reported in the relevant evidence tables. Because numerical value may not convey details about quality assessment, methodological issues pertaining to studies relevant to individual questions are addressed in the discussion of results for each question.