Background To determine if the search technique that is used to sample randomized controlled trial (RCT) manuscripts from a field of medical science can influence the measurement of the change in quality over time in that field. showed significant or near-significant increases over time. Conclusions We exhibited that measuring the change in quality over time of a sample of Ophiopogonin D IC50 RCT manuscripts from the field of brain injury can be greatly affected by the search technique. This poorly recognized factor may make measurements of the change in RCT quality over time within a given field of medical science unreliable. Background Considerable effort has been directed toward improving randomized controlled trial (RCT) design, execution, and reporting [1-6,14]. Such efforts to define standards of quality for RCTs beg the TCF3 question: are RCTs improving in quality over time? Many reviews have attempted to answer this question. In general, these reviews measure the presence or absence of several criteria chosen to define quality in a sample of RCT manuscripts that was selected from a parent populace of RCT manuscripts. The parent populace of RCT manuscripts may be either a field of medical science or a defined part of the medical literature (e.g., RCT manuscripts from a chosen journal). Then, by examining a score of quality as a function of the year-of-publication of the sampled RCT manuscripts, conclusions are drawn as to whether or not quality is usually changing over time in the parent populace of RCTs. If such reviews are to be useful, then, the sample of RCT manuscripts that was chosen for analysis must represent the parent populace of RCT manuscripts. As much as the RCT manuscripts published in a single journal or group of journals would provide a well-defined parent populace, the RCT manuscripts from a given field of medical science would be difficult to completely identify. Ultimately no search strategy can claim to identify all manuscripts on a given topic that have been published in every book and journal worldwide. Thus, two search techniques might provide considerably different samples of RCT manuscripts from the same field of medical science depending upon how much and / or what parts of the parent populace of RCT manuscripts they can access. The current communication empirically demonstrates this Ophiopogonin D IC50 point as a potential pitfall in measuring the change in quality over time of RCT manuscripts sampled from a representative field of medical science. Methods Criteria of quality We selected internal validity as a measure of quality according to the definition given by Gehlbach [7], namely that a RCT is usually internally valid when “within the confines of the study, results appear to be accurate and interpretation of the investigators is usually supported”. We selected criteria of internal validity according to the recommendations of Moher et al. [8]. The relevant points are resolved below. I. Definition of the quality constructWe intended to measure the presence or absence of various criteria of RCT quality as described in the published manuscript. No attempt was made to contact the authors of a manuscript either to clarify the information provided in the manuscript or to gain additional information about a RCT. We acknowledge that relying on the published manuscript Ophiopogonin D IC50 in order to assess the quality of a RCT may be biased (1) against well-designed RCTs that were reported in poorly written manuscripts and (2) in favor of poorly-designed RCTs that were reported in well-written manuscripts [9]. Thus, our scoring process ultimately measured the quality of the report of the RCT manuscript, rather than the true methodological quality of the trial as it was conducted. However, attempting to obtain an understanding of the true methodological quality of a RCT in a retrospective manner by contacting the authors of the manuscripts would undoubtedly collect more information on recent RCTs because their authors will be more Ophiopogonin D IC50 accessible (i.e., less likely to have relocated, retired, or died). Attempting to contact the authors of manuscripts is usually rarely successful [10] and, when it is successful, accurate information about the design and conduct of the RCT is not usually forthcoming [11,12]. II. Definition of the scope of internal validity and identification of quality criteriaAlthough random allocation and the use of a concurrent control group are the sine qua non of the RCT, additional criteria have been so frequently included in their.