Dictionary of Evidence-based Medicine.pdf

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Dictionary of Evidence-based Medicine 19 undertaken. In such a study, cases are identified prospectively but their exposure history to any association between a risk factor (e.g. anorectic agents) and the adverse event (e.g. pulmonary hypertension) is undertaken retrospectively. Case fatality rate The case fatality rate is the rate of death in patients with a particular disease, usually expressed as a percentage (deaths attributed to the disease divided by number of cases of the disease x 100). This rate gives an indication of how deadly a disease is. For example, the case fatality rate for Ebola virus infection is very high while for the influenza virus, it is low except among the elderly. For disease of short duration, the numerators and denominators refer to the same cases. However, with diseases of longer duration, this may not be the case and the measure is no longer a rate but a ratio. For this reason, for diseases such as cancer, the deaths to cases ratio is often quoted instead of case fatality rate. Alternatively, other measures such as five-year survival rates are used. Typically, a group of patients with the same disease is randomized to receive one of the treatments being compared and the percentage of survivors at the end of five years in each subgroup is calculated. Case management Case management is the systematic identification and follow-up of highcost patients so that their care can be co-ordinated through the development of treatment plans to ensure optimum outcome. By definition, costeffectiveness is an important aspect of case management (see also critical pathway and Delaney C, Aquilina D (1987) Case management: meeting the challenge of high cost illness. Employee Benefits Journal. 12: 2-8). Case mix group Case mix groups are groups of patients who are similar in type and consume the same amount of health care resources when expressed as patientdays of care. Categorical variable A variable for which there is only a limited number of possible values and for which there is no logical basis for ordering (e.g. ethnic origin). Alternative names are nominal, polytomous or discrete categorical variable.
20 Dictionary of Evidence-based Medicine Causal relationship In observational studies, the investigator has no control over the factors which may influence a particular outcome and therefore erroneous causal associations may be inferred. To reduce this risk, Bradford Hill has suggested a number of features which should be carefully considered when assessing the causation of a disease: (i) the strength of association; (ii) consistency in the data (in other words, do all or most of the published studies point in the same direction); (iii) specificity; (iv) temporal relationship, i.e. exposure to putative factor must precede onset of disease; (v) biological gradient or dose-response relationship; (vi) biological plausibility. It is important to note, however, that biological plausibility depends on the state of knowledge of the day (Hill AB, Hill ID (1991) Bradford Hill's principles of medical statistics. 12th edn. Edward Arnold, London). Cause-specific rate (see Specific rate) CBA (see Cost benefit analysis) CEA (see Cost-effectiveness analysis) Ceiling effect A ceiling effect is said to occur when a high proportion of subjects in a study have maximum scores on the observed variable. This makes discrimination between subjects at the top end of the scale impossible. For example, an examination paper may lead to, say, 50% of the students scoring 100%. While such a paper may serve as a useful threshold test, it does not allow ranking of the top performers. For this reason, examination of test results for a possible ceiling effect, and the converse floor effect, is often built into the validation of instruments such as those used for measuring quality of life. Censoring Censoring is a phenomenon often seen in the analysis of survival data or event history analyses. To illustrate, consider the follow-up of two groups of terminally ill patients in a comparative study of a new drug and the standard drug. Unfortunately, because we do not have curative drugs for most cancers, time to death is often used as an outcome measure in such
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Page 4 and 5: Preface This book was conceived at
Page 6 and 7: A Ability to pay Ability to pay is
Page 12 and 13: Figure I Audit: Clinical audit cycl
Page 14 and 15: B Balanced design In an experiment,
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Page 72 and 73: G Game theory Game theory, first de
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Dictionary of Evidence-based Medici
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I ICD (see International Classifica
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K Keynes, John Maynard (1883-1946)
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M Macroeconomics Macroeconomics is
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N N of I trial An N of 1 trial is a
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o OBM (see Opinion-based medicine)
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Figure 25 Measuring quality of life
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S Scarcity Scarcity is often referr
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T TDM (see Therapeutic drug monitor
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u Unique value effect This term is
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Z Z variate A random variable which
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