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Systematic Reviews (March 25)
Transcript of Systematic Reviews (March 25)
Keys to Minimize Bias and Maximize Recall Before Starting Data-Analysis Reporting the search methodology Write
a protocol Mining the literature cited by and citing eligible studies Planning and Performing Searches
to Maximize Recall and Minimize Bias Bénédicte Nauche
MUHC Librarian Recall is the sensitivity of the search i.e. the proportion of all relevant articles that are found vs the total number of relevant records in the database. “It is widely believed that valid reviews require as complete as possible an identification of relevant studies, thus recall is the most important search parameter from a scientific perspective. Comprehensive searching, with the objective of high recall, is considered standard practice when conducting systematic reviews.”(Sampson 2006) In the context of a guideline (Raghu G et al. (2011) An Official ATS/ERS/JRS/ALAT Statement: Idiopathic Pulmonary Fibrosis: Evidence-based Guidelines for Diagnosis
and Management. Am J Respir Crit Care Med 183:788-824):
Before the screening At the end of the screening
6376 unique records 46 records were eligible A bias is a systematic error, or deviation from the truth, in results or inferences. Biases can operate in either direction: different biases can lead to underestimation or overestimation of the true intervention effect. (Cochrane Handbook Section 8.2.1) Bias that can occur while conducting a SR has been described (Felson, 1992):
Biases in finding all studies (publication bias, indexing bias, search bias, reference bias, multiple publications bias)
Biases in choosing studies to include (inclusion criteria bias, selector bias)
Obtaining accurate data bias (bias in scoring study quality, outcome reporting bias) Publication bias: Occurs when investigators, reviewers, and editors submit or accept manuscripts for publication based on the direction or strength of the study findings Gray literature bias: Occurs when the results reported in journal articles are systematically different from those presented in other reports, such as working papers, dissertations, or conference abstracts Abstract to full publication bias: Occurs when the full publication of studies that have been initially presented at conferences or in other informal formats is dependent on the direction and/or strength of their findings Search bias: Occurs when there is a bias in captured studies resulting from an inadequate or incomplete search Citation bias: Occurs when the chance of a study being cited by others is associated with its results. Therefore, retrieving literature from scanning reference lists may produce a biased sample of articles, rendering the conclusions of an article less reliable Time-lag bias: Occurs when the speed of publication depends on the direction and strength of the trial results Indexing bias: Occurs when there is biased indexing of published studies in literature databases Plan search
requirements Decide on
eligibility criteria Choose what databases will be searched Formulate
the research questions
the concepts Plan the screening process Pre-search Test and Design Expert Review of Adapt the Search Strategy to Other Database(s) Identify target articles Mine SHs and text words
of target articles Evaluate each text words for
synonyms, spelling variants,
acronyms, abbreviations Test SHs and text words searching AIDS in all text fields retrieves articles about:
visual aids... http://tinyurl.com/cpm36q9 http://tinyurl.com/czf2qka Are there irrelevant articles? Build the complete search strategy in the first database Does the search strategy retrieve target articles? the Search Strategy the Search Strategy http://www.ncbi.nlm.nih.gov/pubmed/22998738 Use advanced search techniques Instead of searching "aids" alone, search (in OvidSP): aids adj5 (virus* or viral or retrovirus or lentivirus or infection* or syndrome*).mp LINK TO TIPSHEET Repeat tests and analysis of results Record each version of the search strategy “Errors that could potentially lower recall of relevant studies were found in 82.5% (median 1, IQR 1.0–2.0) [...] of the search strategies. The most common search errors were missed MeSH terms (44.4%), unwarranted explosion of MeSH terms (38.1%), and irrelevant MeSH or free text terms (28.6%). Missed spelling variants, combining MeSH and free text terms in the same line, and failure to tailor the search strategy for other databases occurred with equal frequency (20.6%). Logical operator error occurred in 19.0% of searches.” (Sampson 2006) SHs, search operators might be different Advanced search process in bibliographic databases “SRs based only on published material may have exaggerated effect sizes, thus gray literature should be included in SRs. Gray literature, such as conference abstracts, should be sought and included, as evidence suggests that “positive” trials presented as abstracts, oral vs. Poster presentations, and RCT designs have a greater likelihood of being published in full” (Tricco 2008) Beyond searching in bibliographic databases Theses Ongoing Research Hand search Conferences Once the screening process is completed, when eligible studies are selected Validation of the search strategy Updating the results prior to the final write-up Screen articles citing eligible studies Screen references in the footnotes and bibliographies of eligible studies Rerun the Medline search strategy Eligible studies From bibliographic databases search From grey literature search or pearlgrowing Check if some studies retrieved were actually indexed in the main bibliographic database.
If there are, analyze why they weren't retrieved through the search strategy. Presuming that other studies might not have been retrieved for the same reason, correct the search strategy in order to make sure they are retrieved, Describe the search strategy in such details it can be replicated: sample strategy, types of studies, approaches, range of years, limits, inclusion / exclusion criteria, terms used, electronic sources.