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The ABC's of medical statistics. Reading and understanding clinical trials
Abstract
Clinical trials test hypotheses that are accepted or rejected according to a predetermined probability of error (level of significance). Significance does not however mean relevance. Good parameters of relevance are absolute risk reduction and based on this the calculation of the number of patients who need to be treated for one additional patient to benefit. The randomized controlled trial is the gold standard for comparative evaluation of effects. In the ideal scenario it is designed so that a difference established by statistical methods becomes probable. In non-inferiority studies care should be taken that no equivalence is shown but rather that the difference is not greater than a predefined margin of error for differences. Meta-analyses of studies with similar endpoints have the potential to improve the level of evidence. Since the findings of meta-analyses depend on the studies included, critical assessment of the results is essential.
... Therefore, we can use flawed cases in research design to explain the principles of statistical design and thereby improve the research design skills of medical students (particularly master's degree students) [22,27,[37][38][39]. We should also combine medical cases and select commonly used advanced statistical analyses for medical research to teach the students, expand their horizons, and enhance their understanding of and ability to apply these difficult statistical methods [17,[40][41][42]. Again, the ability to use statistical software and to apply statistics to practical and clinical applications should be enhanced. ...
Although a substantial number of studies focus on the teaching and application of medical statistics in China, few studies comprehensively evaluate the recognition of and demand for medical statistics. In addition, the results of these various studies differ and are insufficiently comprehensive and systematic.
This investigation aimed to evaluate the general cognition of and demand for medical statistics by undergraduates, graduates, and medical staff in China.
We performed a comprehensive database search related to the cognition of and demand for medical statistics from January 2007 to July 2014 and conducted a meta-analysis of non-controlled studies with sub-group analysis for undergraduates, graduates, and medical staff.
There are substantial differences with respect to the cognition of theory in medical statistics among undergraduates (73.5%), graduates (60.7%), and medical staff (39.6%). The demand for theory in medical statistics is high among graduates (94.6%), undergraduates (86.1%), and medical staff (88.3%). Regarding specific statistical methods, the cognition of basic statistical methods is higher than of advanced statistical methods. The demand for certain advanced statistical methods, including (but not limited to) multiple analysis of variance (ANOVA), multiple linear regression, and logistic regression, is higher than that for basic statistical methods. The use rates of the Statistical Package for the Social Sciences (SPSS) software and statistical analysis software (SAS) are only 55% and 15%, respectively.
The overall statistical competence of undergraduates, graduates, and medical staff is insufficient, and their ability to practically apply their statistical knowledge is limited, which constitutes an unsatisfactory state of affairs for medical statistics education. Because the demand for skills in this area is increasing, the need to reform medical statistics education in China has become urgent.
Many questions in human health research can only be answered with observational studies. In contrast to controlled experiments or well-planned, experimental randomized clinical trials, observational studies are subject to a number of potential problems that may bias their results.
Some of the more important problems affecting observational studies are described and illustrated by examples. Additional information is provided with reference to a selection of the literature.
Factors that may bias the results of observational studies can be broadly categorized as: selection bias resulting from the way study subjects are recruited or from differing rates of study participation depending on the subjects' cultural background, age, or socioeconomic status, information bias, measurement error, confounders, and further factors.
Observational studies make an important contribution to medical knowledge. The main methodological problems can be avoided by careful study planning. An understanding of the potential pitfalls is important in order to critically assess relevant publications.
Systematic reviews systematically evaluate and summarize current knowledge and have many advantages over narrative reviews. Meta-analyses provide a more reliable and enhanced precision of effect estimate than do individual studies. Systematic reviews are invaluable for defining the methods used in subsequent studies, but, as retrospective research projects, they are subject to bias. Rigorous research methods are essential, and the quality depends on the extent to which scientific review methods are used. Systematic reviews can be misleading, unhelpful, or even harmful when data are inappropriately handled; meta-analyses can be misused when the difference between a patient seen in the clinic and those included in the meta-analysis is not considered. Furthermore, systematic reviews cannot answer all clinically relevant questions, and their conclusions may be difficult to incorporate into practice. They should be reviewed on an ongoing basis. As clinicians, we need proper methodological training to perform good systematic reviews and must ask the appropriate questions before we can properly interpret such a review and apply its conclusions to our patients. This paper aims to assist in the reading of a systematic review.
Meta-analysis should be as carefully planned as any other research project, with a detailed written protocol being prepared in advance.The a priori definition of eligibility criteria for studies to be included and a comprehensive search for such studies are central to high quality meta-analysis.The graphical display of results from individual studies on a common scale is an important intermediate step, which allows a visual examination of the degree of heterogeneity between studiesDifferent statistical methods exist for combining the data, but there is no single ''correct'' method.A thorough sensitivity analysis is essential to assess the robustness of combined estimates to different assumptions and inclusion criteria.
The American Journal of Gastroenterology is published by Nature Publishing Group (NPG) on behalf of the American College of Gastroenterology (ACG). Ranked the #1 clinical journal covering gastroenterology and hepatology*, The American Journal of Gastroenterology (AJG) provides practical and professional support for clinicians dealing with the gastroenterological disorders seen most often in patients. Published with practicing clinicians in mind, the journal aims to be easily accessible, organizing its content by topic, both online and in print. www.amjgastro.com, *2007 Journal Citation Report (Thomson Reuters, 2008)
The process of interpreting the results of clinical studies and translating them into clinical practice is being debated. Here we examine the role of p values and confidence intervals in clinical decision-making, and draw attention to confusion in their interpretation. To improve result reporting, we propose the use of confidence levels and plotting of clinical significance curves and risk-benefit contours. These curves and contours provide degrees of probability of both the potential benefit of treatment and the detriment due to toxicity. Additionally, they provide clinicians with a mechanism of translating the results of studies into treatment for individual patients, thus improving the clinical decision-making process. We illustrate the application of these curves and contours by reference to published studies. Confidence levels, clinical significance curves, and risk-benefit contours can be easily calculated with a hand calculator or standard statistical packages. We advocate their incorporation into the published results of clinical studies.
Traditionally, randomized controlled trials (RCTs) have attempted to show the superiority of one intervention over another. However, when effective treatment already exists, it is sometimes more useful to prove that an intervention is equivalent, or at least not inferior, to the standard of care. Our aim was to determine whether claims of equivalency in digestive diseases trials are supported by the evidence.
Medline was searched for RCTs published between 1989 and 2002 using the MeSH headings "exp therapeutic equivalency" and "exp digestive diseases" and the text words "equivalence," "equal," "equals," or "equivalent," yielding 902 articles. Of these, 73 articles met the inclusion criteria. These articles were evaluated using previously published criteria for equivalency.
Of the included articles, 33% stated an a priori research aim of equivalency, 92% reported differences of <20% between "equal" interventions, 34% set an equivalency boundary and tested it appropriately, and 19% performed a sample size calculation for equivalency. Overall, 12% of the reviewed articles met all 5 criteria. Fifty-two percent of our sample inappropriately used a failed superiority test (i.e., a P value > 0.05) as statistical "proof" of equivalency. Nonsurgical trials and those published between 1996 and 2002 were more likely to meet criteria than were surgical trials (P = 0.07) or trials published before 1996 (P = 0.003).
Claims of equivalency between interventions in digestive diseases trials tend to be poorly supported by the evidence. Erroneous claims of equivalency are potentially dangerous and may lead to substandard patient care.
The American Journal of Gastroenterology is published by Nature Publishing Group (NPG) on behalf of the American College of Gastroenterology (ACG). Ranked the #1 clinical journal covering gastroenterology and hepatology*, The American Journal of Gastroenterology (AJG) provides practical and professional support for clinicians dealing with the gastroenterological disorders seen most often in patients. Published with practicing clinicians in mind, the journal aims to be easily accessible, organizing its content by topic, both online and in print. www.amjgastro.com, *2007 Journal Citation Report (Thomson Reuters, 2008)
The American Journal of Gastroenterology is published by Nature Publishing Group (NPG) on behalf of the American College of Gastroenterology (ACG). Ranked the #1 clinical journal covering gastroenterology and hepatology*, The American Journal of Gastroenterology (AJG) provides practical and professional support for clinicians dealing with the gastroenterological disorders seen most often in patients. Published with practicing clinicians in mind, the journal aims to be easily accessible, organizing its content by topic, both online and in print. www.amjgastro.com, *2007 Journal Citation Report (Thomson Reuters, 2008)