Traditional reviews, meta-analyses and pooled analyses in epidemiology.
BACKGROUND: The use of review articles and meta-analysis has become an important part of epidemiological research, mainly for reconciling previously conducted studies that have inconsistent results. Numerous methodologic issues particularly with respect to biases and the use of meta-analysis are still controversial. METHODS: Four methods summarizing data from epidemiological studies are described. The rationale for meta-analysis and the statistical methods used are outlined. The strengths and limitations of these methods are compared particularly with respect to their ability to investigate heterogeneity between studies and to provide quantitative risk estimation. RESULTS: Meta-analyses from published data are in general insufficient to calculate a pooled estimate since published estimates are based on heterogeneous populations, different study designs and mainly different statistical models. More reliable results can be expected if individual data are available for a pooled analysis, although some heterogeneity still remains. Large prospective planned meta-analysis of multicentre studies would be preferable to investigate small risk factors, however this type of meta-analysis is expensive and time-consuming. CONCLUSION: For a full assessment of risk factors with a high prevalence in the general population, pooling of data will become increasingly important. Future research needs to focus on the deficiencies of review methods, in particular, the errors and biases that can be produced when studies are combined that have used different designs, methods and analytic models. (+info)
Erythropoietin and platelet production.
BACKGROUND AND OBJECTIVE: Erythropoietin (Epo) is the primary growth factor for the red cell lineage but treatment with recombinant human Epo (rHuEpo) has been shown to increase platelet counts. In several animal species treatment with rHuEpo stimulated platelet production, but platelet counts tended to normalize after 1-2 weeks and large, chronic doses even caused thrombocytopenia. This paper aims to review the evidence about the effects of Epo on megakaryopoiesis. INFORMATION SOURCES: I examined the literature published in journals covered by Medline(R)a concerning the effects of Epo, hypoxia and iron deficiency on megakaryopoiesis and platelets. The reference list of each article was reviewed to try to identify further contributions. STATE OF THE ART: In vivo data have shown that moderate Epo stimulation, i.e. that produced by standard doses of rHuEpo, short-term hypoxia or moderate iron deficiency, causes a moderate elevation of platelet counts, whereas intense Epo stimulation, as produced by high doses of rHuEpo, prolonged hypoxia or severe iron deficiency, causes some degree of thrombocytopenia. In the latter case, there appears to be a diphasic response to Epo, the initial positive response (a stimulation of platelet production) being followed by thrombocytopenia. Contrarily to the thrombocytopenia due to increased platelet destruction induced by other growth factors, Epo-induced thrombocytopenia is the result of an inhibition of platelet production. CONCLUSION AND PERSPECTIVE: Stem-cell competition between erythroid and platelet precursors appears to be the cause of these phenomena in situations of prolonged, intense stimulation by Epo. In vitro data support the existence of a common erythrocytic and megakaryocytic precursor. It remains to be determined whether these effects of rHuEpo are a result of the dose itself or of the magnitude of the erythropoietic effect of that dose. It is not known whether a lower dose given in a patient with decreased marrow function would bring about the same biological effects as those induced by high doses of rHuEpo in the presence of a normal marrow function. Caution should be exercised before using high doses of hematopoietic growth factors. (+info)
Systematic reviews and meta-analyses on treatment of asthma: critical evaluation.
OBJECTIVE: To evaluate the clinical, methodological, and reporting aspects of systematic reviews and meta-analyses on the treatment of asthma and to compare those published by the Cochrane Collaboration with those published in paper based journals. DESIGN: Analysis of studies identified from Medline, CINAHL, HealthSTAR, EMBASE, Cochrane Library, personal collections, and reference lists. STUDIES: Articles describing a systematic review or a meta-analysis of the treatment of asthma that were published as a full report, in any language or format, in a peer reviewed journal or the Cochrane Library. MAIN OUTCOME MEASURES: General characteristics of studies reviewed and methodological characteristics (sources of articles; language restrictions; format, design, and publication status of studies included; type of data synthesis; and methodological quality). RESULTS: 50 systematic reviews and meta-analyses were included. More than half were published in the past two years. Twelve reviews were published in the Cochrane Library and 38 were published in 22 peer reviewed journals. Forced expiratory volume in one second was the most frequently used outcome, but few reviews evaluated the effect of treatment on costs or patient preferences. Forty reviews were judged to have serious or extensive flaws. All six reviews associated with industry were in this group. Seven of the 10 most rigorous reviews were published in the Cochrane Library. CONCLUSIONS: Most reviews published in peer reviewed journals or funded by industry have serious methodological flaws that limit their value to guide decisions. Cochrane reviews are more rigorous and better reported than those published in peer reviewed journals. (+info)
The building blocks of evidence-based dentistry.
The practice of dentistry is becoming more complex and challenging. Changing socio-demographic patterns, patients as knowledgeable health care consumers, rapid technical advances and the information "explosion" all place greater demands on clinical decision making. The need for reliable information and the electronic revolution have come together to allow the "paradigm shift" towards evidence-based health care to progress swiftly. Evidence-based dentistry closes the gap between clinical research and real world dental practice and provides dentists with powerful tools to interpret and apply research findings. Central to evidence-based practice is the systematic literature review, which synthesizes the best evidence and provides the basis for clinical practice guidelines. (+info)
Evidence based medicine in practice: lessons from a Scottish clinical genetics project.
OBJECTIVE: To establish national clinical guidelines and integrated care pathways for five conditions (tuberous sclerosis (TS), Huntington's disease (HD), myotonic dystrophy (MD), neurofibromatosis type 1 (NF1), and Marfan syndrome (MS)) and audit their use in Scotland. DESIGN: Systematic review of published reports followed by consensus conferences to prepare clinical guidelines and integrated care pathways. Structured review of medical records before and after introduction of integrated care pathways to document changes in practice. Survey of staff views on procedures adopted. SETTING: All four clinical genetics centres in Scotland. RESULTS: Project resulted in reduced variation in practice across centres, improved data recording in medical records, and improved communication with other professional groups. A very poor evidence base for management of patients with the conditions studied was found. CONCLUSIONS: A collaborative structure for undertaking clinical research would improve the evidence base for current practice. National discussion of the boundaries of responsibility of care for the long term management of patients with these disorders is required. The integrated care pathway approach shows promise as a means of facilitating the development of audit within clinical genetics services. (+info)
Clarifying the abstracts of systematic literature reviews.
BACKGROUND: There is a small body of research on improving the clarity of abstracts in general that is relevant to improving the clarity of abstracts of systematic reviews. OBJECTIVES: To summarize this earlier research and indicate its implications for writing the abstracts of systematic reviews. METHOD: Literature review with commentary on three main features affecting the clarity of abstracts: their language, structure, and typographical presentation. CONCLUSIONS: The abstracts of systematic reviews should be easier to read than the abstracts of medical research articles, as they are targeted at a wider audience. The aims, methods, results, and conclusions of systematic reviews need to be presented in a consistent way to help search and retrieval. The typographic detailing of the abstracts (type-sizes, spacing, and weights) should be planned to help, rather than confuse, the reader. (+info)
Evidence-based medicine in nephrology: identifying and critically appraising the literature.
BACKGROUND: Uncertainties about best management of end-stage renal disease (ESRD) are reflected in wide variations in practice. Systematic reviews aim to reduce uncertainty by strengthening the evidence base for clinical practice, allowing estimation of the benefits and risks of particular interventions, whilst minimizing the potential for bias. This paper describes the methods and conduct of six systematic reviews of aspects of the management of ESRD, and the yield in terms of trials found. METHODS: Our methodology was based on that recommended by the Cochrane Collaboration (an international initiative set up to perform and disseminate systematic reviews of health care). It involved a systematic search of electronic databases and bibliographic reference lists, together with handsearching of Kidney International for studies relevant to the management of ESRD, followed by a systematic assessment of study quality. RESULTS: Around 12,000 abstracts were assessed which had been identified from electronic sources. Of these, 2085 (18%) were deemed to be reports of possible randomized or quasi-randomized controlled trials relevant to the management of ESRD. Three hundred and forty were relevant to the six specific reviews, and after assessment of the full manuscripts, 39 studies were finally included in our reviews. Reports of a further nine trials, which were identified from other sources, were also included. The broad search adopted allowed the parallel development of a register of trials of all aspects of the management of ESRD. CONCLUSIONS: This study has demonstrated that the methodology of systematic reviews, as promoted by the Cochrane Renal Group, is feasible but has significant resource implications. The development of a register of randomized controlled trials (RCTs) related to the management of ESRD will facilitate this form of research in the future. (+info)
Comparison of information processing technologies.
OBJECTIVE: To examine the type of information obtainable from scientific papers, using three different methods for the extraction, organization, and preparation of literature reviews. DESIGN: A set of three review papers was identified, and the ideas represented by the authors of those papers were extracted. The 161 articles referenced in those three reviews were then analyzed using 1) a formalized data extraction approach, which uses a protocol-driven manual process to extract the variables, values, and statistical significance of the stated relationships; and 2) a computerized approach known as "Idea Analysis," which uses the abstracts of the original articles and processes them through a computer software program that reads the abstracts and organizes the ideas presented by the authors. The results were then compared. The literature focused on the human papillomavirus and its relationship to cervical cancer. RESULTS: Idea Analysis was able to identify 68.9 percent of the ideas considered by the authors of the three review papers to be of importance in describing the association between human papillomavirus and cervical cancer. The formalized data extraction identified 27 percent of the authors' ideas. The combination of the two approaches identified 74.3 percent of the ideas considered important in the relationship between human papillomavirus and cervical cancer, as reported by the authors of the three review articles. CONCLUSION: This research demonstrated that both a technically derived and a computer derived collection, categorization, and summarization of original articles and abstracts could provide a reliable, valid, and reproducible source of ideas duplicating, to a major degree, the ideas presented by subject specialists in review articles. As such, these tools may be useful to experts preparing literature reviews by eliminating many of the clerical-mechanical features associated with present-day scientific text processing. (+info)