Objectives: The purpose of this study was to determine whether the number of bibliographic databases used to search the health sciences literature in individual systematic reviews (SRs) and meta-analyses (MAs) changed over a twenty-year period related to the official 1995 launch of the Cochrane Database of Systematic Reviews (CDSR).Methods: Ovid MEDLINE was searched using a modified version of a strategy developed by the Scottish Intercollegiate Guidelines Network to identify SRs and MAs. Records from 3 milestone years were searched: the year immediately preceding (1994) and 1 (2004) and 2 (2014) decades following the CDSR launch. Records were sorted with randomization software. Abstracts or full texts of the records were examined to identify database usage until 100 relevant records were identified from each of the 3 years. They employ reproducible methodology to identify all relevant studies, assess the validity of their findings, and combine the results to provide conclusive answers to clinical questions [3]. Once the literature has been systematically reviewed, quantitative data from individual studies may be pooled and reanalyzed using established statistical methods [4]. These reports are called meta-analyses (MAs), which are considered a subtype of SRs. The rationale for MAs is that combining samples of individual studies increases overall sample size, thereby improving the statistical power of the analysis and the precision of the estimates of treatment effects [5]. SRs and MAs are foundations of evidence-based medicine, as they rely on balanced inference generated from collated evidence instead of commentaries made by experts, as in the case of narrative reviews [6]. SRs and MAs have become increasingly popular for providing evidence of the effectiveness of medical interventions to support the creation of clinical practice guidelines. In 2010, an average of eleven new SRs or MAs were published each day [7].High-quality SRs require high-quality literature searches and accurate reporting. Searching a single database identifies a maximum of one-third of all relevant articles, and searching more databases may identify only half of all available articles [8]. A search conducted solely in MEDLINE results in database bias, as only 30%-80% of all trials are identifiable through MEDLINE [9]. Although the Cochrane 284

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ObjectivesThe research tested the authors’ hypothesis that more researchers from the academic medicine community in the United States and Canada with institutional access to Embase had started using Embase to replace MEDLINE since Embase was expanded in 2010 to cover all MEDLINE records.MethodsWe contacted libraries of 140 and 17 medical schools in the United States and Canada, respectively, to confirm their subscriptions to Embase 5 years before and 5 years after 2010. We searched the names of institutions with confirmed Embase access in Ovid MEDLINE and Embase to retrieve works authored by affiliates of those institutions. We then examined 100 randomly selected records from each of the 5 years before and 5 years after the Embase coverage expansion in 2010. We hypothesized that studies that used Embase but not MEDLINE would increase due to the Embase coverage expansion.ResultsThe number of studies that used Embase but not MEDLINE did not change between the pre-2010 and post-2010 periods.ConclusionOur hypothesis was refuted. Studies that used Embase but not MEDLINE did not increase post-2010. Our results suggest the academic medicine community in the United States and Canada that had access did not use Embase to replace MEDLINE, despite the Embase coverage expansion.

Although serial transcranial Doppler measurements of blood flow velocity are of considerable clinical utility, their use assumes that the velocity signals are stable and unchanging during short time periods. Contrary to this assumption, the authors found significant variations in mean velocity signals in both normal subjects and patients, which may confound the interpretation of serial studies. Signals were continuously obtained for 5 to 10 minutes from the middle cerebral artery of 11 normal subjects and 18 patients (22 studies) with a variety of neurosurgical disorders. The average difference between the peak and the trough in the waves observed in the normal population was 11 +/- 4% (standard error of mean), and 5 of the 11 had at least one wave with a difference of more than 20%. The average difference between the peak and trough signals in the neurosurgical population was 14 +/- 13% (SEM) and 13 of the 22 studies showed at least one wave with a difference of more than 20%. These variations were consistently seen and may be related to similar variations in blood pressure or intracranial pressure waves. Whatever the origin, these variations should be recognized during the interpretation of transcranial Doppler signal in clinical practice.

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