Evidence-Based Medicine Working Group Research Articles

Letters to the Editor

To the Editor: —McGee1 does a service for us by focusing on the likelihood ratio as one of—if not the most important—operating characteristic of a diagnostic test. He suggests that its lack of use is due to the burdensome calculations necessary for conversion between odds and probabilities. Although this may be true, we offer an alternative explanation. Probabilities differ from likelihoods in important ways.2 With probabilities, the data are random and hypotheses are fixed, allowing one to develop conditional probabilities. Conversely, with likelihoods, the data are fixed and the hypotheses are random, as seen in a differential diagnosis. Likelihoods do not follow the rules of probability theory. Odds have made intuitive sense to the man on the street who bets on categorical events like winning a horserace. Odds also apply to such things as whether a solitary pulmonary nodule is malignant or benign or if a woman is pregnant or not. That we in medicine have chosen to remain with probabilities and dismiss odds shows that we have yet to grasp this subtle but important distinction. With respect to an interpretation of likelihood ratios such as that given in McGee's Table 2, Jaeschke et al. 3 from the Evidence-Based Medicine Working Group note the following: “Likelihood ratios greater than 10 or less than 0.1 generate large and often conclusive changes from pretest to post-test probability. Likelihood ratios of 5 to 10 and 0.1 to 0.2 generate moderate shifts in pretest to posttest probability. Likelihood ratios of 2 to 5 and 0.2 to 0.5 generate small (but sometimes important) changes in probability. Likelihood ratios of 1 to 2 and 0.5 to 1 alter probability to a small (and rarely important) degree.” The divergent relationship between odds and probabilities is important in decision-making involving probabilities less than 10% and greater than 90%. If a man has a solitary pulmonary nodule with a 50% probability (odds of 1) of malignancy, would his doctor and he want a hypothetical test that had a likelihood ratio of 13 or one with 101 to rule it in? If the first test was positive, the probability would be 93%, compared with a probability of 99% with a positive second test—a mere difference of 6%. Using odds, after a positive first test, he would have 13 chances of having the malignancy to 1 chance of its being benign, whereas with the second test positive, his odds increase to 101 chances of having a cancer to 1 not. This example involves probability ranges beyond the formula proposed by McGee. Dreyfus and Dreyfus4 have shown that the novice makes decisions in a protracted and laborious manner, using context-free rules, with no base of experience, having no responsibility for the problem, and using conscious analysis. Conversely, the expert gathers information fluently and expeditiously by focusing on the situation at hand, using his or her base of experience, having a strong sense of responsibility that drives an intuitive decision. The range suggested by McGee limits us to probabilities between 10% (odds 1 to 9) and 90% (odds 9 to 1), in which an intuitive sense is meager. While this is sufficient for decisions regarding appendicitis or streptococcal pharyngitis, it is inadequate in dealing with problems such as malignancy.—John C. Peirce, MD, MA, MS, Richard D. Gerkin, MD, MS,Good Samaritan Regional Medical Center, Phoenix, Ariz.

The impact of geriatric post-discharge services on mental state.

To determine the impact of geriatric post-discharge services on mental state. Three computer databases, MEDLINE, HealthSTAR and the Cochrane Database of Systematic Reviews were searched for relevant articles; the bibliographies of retrieved articles were searched for additional references. 11 trials were located that met the four inclusion criteria: (i) original study; (ii) published in English or French; (iii) controlled trial (randomized or non-randomized) of a geriatric post-discharge service; and (iv) including at least one measure of mental state. All trials met most of the validity criteria for intervention studies of the Evidence-Based Medicine Working Group. Three trials reported a small effect on emotional state or self-perceived health and eight trials reported no effect. There is little evidence that geriatric post-discharge services have an impact on the mental state of aged subjects. Future services and studies should be designed to address the issue of mental state outcomes in this population.

Feedback: Computed tomography for subarachnoid hemorrhage

Feedback: Computed tomography for subarachnoid hemorrhage

Evidence-based medicine: principles for applying the users’ guides to patient care. Guyatt GH,∗ Haynes RB, Jaeschke RZ, Cook DJ, Green L, Naylor CD, Wilson MC, Richardson WS for the Evidence-Based Medicine Working Group. JAMA 2000;284:1290–1296.

Evidence-based medicine: principles for applying the users’ guides to patient care. Guyatt GH,∗ Haynes RB, Jaeschke RZ, Cook DJ, Green L, Naylor CD, Wilson MC, Richardson WS for the Evidence-Based Medicine Working Group. JAMA 2000;284:1290–1296.

Users' guides to the medical literature: XXIV. How to use an article on the clinical manifestations of disease. Evidence-Based Medicine Working Group.

Clinicians rely on knowledge about the clinical manifestations of disease to make clinical diagnoses. Before using research on the frequency of clinical features found in patients with a disease, clinicians should appraise the evidence for its validity, results, and applicability. For validity, 4 issues are important-how the diagnoses were verified, how the study sample relates to all patients with the disease, how the clinical findings were sought, and how the clinical findings were characterized. Ideally, investigators will verify the presence of disease in study patients using credible criteria that are independent of the clinical manifestations under study. Also, ideally the study patients will represent the full spectrum of the disease, undergo a thorough and consistent search for clinical findings, and these findings will be well characterized in nature and timing. The main results of these studies are expressed as the number and percentages of patients with each manifestation. Confidence intervals can describe the precision of these frequencies. Most clinical findings occur with only intermediate frequency, and since these frequencies are equivalent to diagnostic sensitivities, this means that the absence of a single finding is rarely powerful enough to exclude the disease. Before acting on the evidence, clinicians should consider whether it applies to their own patients and whether it has been superseded by new developments. Detailed knowledge of the clinical manifestations of disease should increase clinicians' ability to raise diagnostic hypotheses, select differential diagnoses, and verify final diagnoses. JAMA. 2000;284:869-875

Users' guides to the medical literature: XXIII. Qualitative research in health care B. What are the results and how do they help me care for my patients? Evidence-Based Medicine Working Group.

The second part of this 2-part series on how to interpret qualitative research addresses, "what are the results," and, "how do they help me care for my patients?" Qualitative analysis is a process of summarizing and interpreting data to develop theoretical insights that describe and explain social phenomena such as interactions, experiences, roles, perspectives, symbols, and organizations. Key results are often illustrated with excerpts from interview transcripts, field notes, or documents. The results of a qualitative research report are best understood as an empirically based contribution to ongoing dialogue and exploration. Empirically based theory evolves from a process of exploration, discovery, analysis, and synthesis. Each concept should be defined carefully in a way that is meaningful to the reader. Concepts should be adequately developed and illustrated when theoretical conclusions are drawn. Arguments should be explained and justified. The qualitative research report ideally should address how the findings relate to other theories in the field. The qualitative study can provide a useful road map for understanding and navigating similar social settings interactions, or relationships. JAMA. 2000;284:478-482

Users' guides to the medical literature: XXII: how to use articles about clinical decision rules. Evidence-Based Medicine Working Group.

Clinical experience provides clinicians with an intuitive sense of which findings on history, physical examination, and investigation are critical in making an accurate diagnosis, or an accurate assessment of a patient's fate. A clinical decision rule (CDR) is a clinical tool that quantifies the individual contributions that various components of the history, physical examination, and basic laboratory results make toward the diagnosis, prognosis, or likely response to treatment in a patient. Clinical decision rules attempt to formally test, simplify, and increase the accuracy of clinicians' diagnostic and prognostic assessments. Existing CDRs guide clinicians, establish pretest probability, provide screening tests for common problems, and estimate risk. Three steps are involved in the development and testing of a CDR: creation of the rule, testing or validating the rule, and assessing the impact of the rule on clinical behavior. Clinicians evaluating CDRs for possible clinical use should assess the following components: the method of derivation; the validation of the CDR to ensure that its repeated use leads to the same results; and its predictive power. We consider CDRs that have been validated in a new clinical setting to be level 1 CDRs and most appropriate for implementation. Level 1 CDRs have the potential to inform clinical judgment, to change clinical behavior, and to reduce unnecessary costs, while maintaining quality of care and patient satisfaction. JAMA. 2000;284:79-84

Prognosis of depression in elderly community and primary care populations: a systematic review and meta-analysis.

The purpose of this study was to determine the prognosis of depression in elderly community and primary care populations. MEDLINE and PsycINFO were searched for potentially relevant articles published from January 1981 to November 1996 and from January 1984 to November 1996, respectively. The bibliographies of relevant articles were searched for additional references. Twelve studies met the following five inclusion criteria: original research, published in English or French, study population of community residents or primary care patients, subjects' mean age 60 years and over, and reported affective state as an outcome. The validity of the studies was assessed according to the criteria for prognostic studies described by the Evidence-Based Medicine Working Group. Information about the population, proportion of depressed subjects detected and treated by primary care physicians, length of follow-up, outcomes, and prognostic factors was systematically abstracted from each report. All of the studies had some methodologic limitations. A meta-analysis of outcomes at 24 months estimated that 33% of subjects were well, 33% were depressed, and 21% had died. There was statistically significant heterogeneity in the outcomes across studies. The length of follow-up and lower age limit for enrollment explained part of the heterogeneity for the percent well but not for the other outcomes. Physical illness, disability, cognitive impairment, and more severe depression were associated with worse outcomes but inconsistently so. Depression in elderly community and primary care populations has a poor prognosis, is perhaps chronic or relapsing or both, and is probably undertreated. Despite the methodologic limitations of the studies and this meta-analysis, these findings seem to support efforts to develop detection and treatment programs for depression in these populations.

Users' guides to the medical literature: XVII. How to use guidelines and recommendations about screening. Evidence-Based Medicine Working Group.

Users' guides to the medical literature: XVII. How to use guidelines and recommendations about screening. Evidence-Based Medicine Working Group.

Evidence-Based Medicine: A New Paradigm for the Teaching and Practice of Medicine

Evidence-Based Medicine: A New Paradigm for the Teaching and Practice of Medicine

Editorial: Thromboembolic Complications After Fontan Procedures—The Role Of Prophylactic Anticoagulation

Editorial: Thromboembolic Complications After Fontan Procedures—The Role Of Prophylactic Anticoagulation

Impact of geriatric home screening services on mental state: a systematic review.

The purpose of this report was to determine the impact of geriatric home screening services on mental state. Two computer databases, MEDLINE and HealthSTAR, were searched for relevant articles published from January 1975 to June 1997, and the bibliographies of retrieved articles were searched for additional references. Seven trials were located that met the four inclusion criteria: (a) original study; (b) published in English or French; (c) controlled trial (randomized or nonrandomized) of a geriatric home screening service; and (d) the trial included at least one measure of mental state. All trials met most of the validity criteria for intervention studies of the Evidence-Based Medicine Working Group. Two trials reported a small effect on morale or self-perceived health and five trials reported no effect. Thus, there was little evidence that geriatric home screening services had an impact on the mental state of aged subjects.

Evidence-Based Medicine—How to Practice and Teach EBM. D. L. Sackett, W. S. Richardson, W. Rosenberg, and R. B. Haynes. New York: Churchill Livingstone, 1997, 250 pp. Paperback, $24.99. ISBN 0-443-05686-2.

Regular readers of JAMA will have noted an on-going series with the catchy title “Users’ Guide to the Medical Literature” emanating from the Evidence-Based Medicine Working Group. One article from the series [Jaeschke R, Guyatt GH, Sackett DL. Users guide to the medical literature. III. How to use an article about a diagnostic test. B. What are the results and will they help me in caring for my patients? JAMA 1994;271:703–7] would be of particular interest to readers of Clinical Chemistry and has important implications for all clinical laboratory workers who interface with clinicians. If a Bayesian cardiologist were to inquire about the likelihood ratio for different concentrations of CK-MB or troponin following an infarction, could the laboratory scientist provide this information or know …

Evidence-based medicine and the journal club: a cross-sectional survey of participants' views

1997). Although this view is gaining ground, journal clubs remain a fundamental part of postgraduate education, both from the point of view of continuing medical education for con sultants and the education of trainees. There are problems with the traditional journal club format: the paper may be selected ad hoc and may not be the most suitable to cover the topic in question; the trainee may have no say in the choice of paper, not know why the paper has been chosen and have little interest in the topic; often, trainees prA©cisa paper, and offer an unstructured and poorly performed critique; trainees get no experience of reviewing a ques tion or undertaking a literature search. For these reasons, the whole process can be very boring for the audience and presenter alike, and limited in terms of learning. In an attempt to overcome these difficulties, an alternative approach would be to adopt the evidencebased medicine (EBM) paradigm (Gilbody, 1996; Sackett et al, 1997). Evidence-based medicine, defined as the conscientious, explicit and judi cious use of current best evidence in making decisions about the care of individual patients (Sackett et al 1996), has been suggested as a new approach to teaching the practice of medicine (Evidence-Based Medicine Working Group. 1992). From the point of view of an academic programme, the EBM approach could involve integrating the case conference with the journal club; the paper presented at the latter chosen to address a question or topic arising from the case.

Users' guides to the medical literature. XIII. How to use an article on economic analysis of clinical practice. B. What are the results and will they help me in caring for my patients? Evidence-Based Medicine Working Group.

Users' guides to the medical literature. XIII. How to use an article on economic analysis of clinical practice. B. What are the results and will they help me in caring for my patients? Evidence-Based Medicine Working Group.

Users' guides to the medical literature. XIII. How to use an article on economic analysis of clinical practice. A. Are the results of the study valid? Evidence-Based Medicine Working Group.

Users' guides to the medical literature. XIII. How to use an article on economic analysis of clinical practice. A. Are the results of the study valid? Evidence-Based Medicine Working Group.

Users' guides to the medical literature. XII. How to use articles about health-related quality of life. Evidence-Based Medicine Working Group.

Users' guides to the medical literature. XII. How to use articles about health-related quality of life. Evidence-Based Medicine Working Group.

Users' guides to the medical literature. XI. How to use an article about a clinical utilization review. Evidence-Based Medicine Working Group.

Users' guides to the medical literature. XI. How to use an article about a clinical utilization review. Evidence-Based Medicine Working Group.

Users' guides to the medical literature. X. How to use an article reporting variations in the outcomes of health services. The Evidence-Based Medicine Working Group

Users' guides to the medical literature. X. How to use an article reporting variations in the outcomes of health services. The Evidence-Based Medicine Working Group

Users' guides to the medical literature. IX. A method for grading health care recommendations. Evidence-Based Medicine Working Group

Users' guides to the medical literature. IX. A method for grading health care recommendations. Evidence-Based Medicine Working Group