Clinical Trials

❘❙❚■ Chapter 38 | Meta-AnalysisTable 2. Sources of information for meta-analyses.• Search for peer-reviewed material in electronic medical databases, such as:– MEDLINE (including Pre-MEDLINE)– Embase– BIDS– ISI– The Cochrane Collaboration Library• Review published books that are relevant to the subject or conference material from meetings devoted to thesubject, such as abstract books• Search specific Internet sites relevant to the disease, including national and international societies of specialists(for beta-blockers, the American College of Cardiology or the European Society of Cardiology web sites) andclearing houses of guidelines for the treatment of that disease/condition• National or local registries and further unpublished studies can also contribute to the meta-analysis.For these, approach recognized experts and leading medical centers in the specific disease area• Communicate with the research and clinical affairs departments of specialist pharmaceutical companiesto gain published or unpublished study data• Do a general search of Internet sites using medical search engines, such as OMNI, and general search enginessuch as:– www.Google.com– www.AltaVista.com– www.Yahoo.comStep 2: Literature searchTo answer the study question, it is important to capture as many relevant studiesas possible. The methods used to gather information for a meta-analysis are shownin Table 2.In the beta-blocker study we used a computerized bibliographic method to searchthe MEDLINE database from January 1998–January 2000 using keywordsand phrases such as ‘beta-blocker’, ‘clinical trials’, and ‘congestive heart failure’.We also searched reports of abstracts from conferences on cardiology and heartfailure for the period of 1996–2000.Step 3: Study selectionOnly studies that have a similar design can be retained from all of the studiesidentified. While formal match-scoring systems (systems to evaluate how similarthe studies are) exist and can allow us to control the contribution that a studymakes to the meta-analysis, some simple criteria can be used to match the studiesto be combined. These are as follows:• trial design, eg, parallel versus crossover, randomized controlled trials(RCTs) versus non-RCTs• included patient populations, eg, heart failure patients with or withoutcoronary artery disease442