Dictionary of Evidence-based Medicine.pdf

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Dictionary of Evidence-based Medicine 17 reduces noise and enables the effects of other factors to be estimated with greater precision (Maxwell SE, Delaney HD (1990) Designing experiments and analysing data. Wadsworth, Belmont, California). Bootstrapping Bootstrapping is a computer-based approach for assigning measures of accuracy to statistical estimates. The method is non-parametric in that it does not assume anything about the underlying probability distribution. The idea behind bootstrapping is elegantly simple. Consider some population of size n about which we wish to make some inference. Let X = (x v x 2/ x 3 ,... f n) represent the data points and suppose that we wanted to estimate the standard error of the median. We can draw a bootstrap sample of the same size from X by sampling one point with replacement and repeating this n times. For example, with n = 6, we might obtain a bootstrap sample (x v x v x y x y x 6 , x 6 ). From these points we can calculate a sample standard deviation. We can repeat the process to obtain m bootstrap samples and m standard deviations. The standard deviation of those sample standard deviations will then give us a bootstrap estimate of the standard error of the median (Efron B, Tibshirani RJ (1993) An introduction to the bootstrap. Chapman and Hall, London). Boundary approach This is an approach to running and analysing sequential trials whereby a statistic describing the cumulative difference between treatments is plotted against a statistic describing the cumulative amount of evidence. The trial is stopped if one of the pre-specified boundaries is crossed (Whitehead J (1992) The design and analysis of sequential trials. 2nd edn. Ellis Horwood, Chichester).
C CANDA CANDA is the abbreviation used for computer-assisted new drug application, a procedure which was introduced by the FDA recently (see Prescription Drug User Fee Act 1992) to speed up the review process of licensing of new drugs. Carstairs score (see under Cluster sampling) Case-control study In the study of rare events, for example rare adverse drug reactions, it is usually not possible to mount a controlled study to investigate causation. Impossibly large numbers of subjects would have to be recruited and studied under controlled conditions. Under such circumstances observational studies are used. One of the most powerful designs for such studies, albeit not ideal because of the poor control investigators have over confounding factors, is the case-control design. Cases or subjects with the event of interest (e.g. women of childbearing age and with a stroke) are recruited along with matched control subjects without the event and their history of exposures to various putative risk and confounding factors detailed to identify any significant associations. Case-control studies are normally classified as retrospective studies in that subjects with a particular event (e.g. a stroke) are identified and their history of exposure to various putative risk factors established retrospectively and compared with that of control subjects. Case-control studies leading to the establishment of a link between phaecomelia in newborns and ingestion of thalidomide by their mothers is an example. The cases were already known and the drug history of their mothers and that of control mothers followed retrospectively. It would clearly not have been ethical to undertake a controlled study to establish the causal association. The adverse effect was not previously seen and was disastrous. In other types of adverse effects, for example pulmonary hypertension, case ascertainment may be difficult and a prospective case-control study may then be
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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
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Page 14 and 15: B Balanced design In an experiment,
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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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