Dictionary of Evidence-based Medicine.pdf

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Dictionary of Evidence-based Medicine 141 predicted y value from the straight line equation. The difference between that value and the observed value is the residual error. Resource intensity weights Resource intensity weights are weights developed to capture the intensity of resource utilization by individual case mix groups (Baladi JF (1996) A guidance document for the costing process. Canadian Coordinating Office for Health Technology Assessment, Ottawa, http://www.ccohta.ca). Response expectancy The effect of patients' prior expectation of the efficacy of treatments being evaluated on their observed responses to those treatments. For example, it has been observed that when patients are administered a placebo, if they are told to expect an active treatment, then their response is different to that seen when they are told that they will receive either an active treatment or a placebo. Similarly, the design of a study may affect response rate, a phenomenon probably partially attributable to response expectancy (Kirsch I, Weixel LJ (1992) Double-blind versus deceptive administration of a placebo. Behavioural Neuroscience. 102: 319-23. Colditz GA, Miller JN, Mosteller F (1988) The effect of study design on gain in the evaluation of new treatments in medicine and surgery. Drug Information Journal. 22: 343-52). Retrospective study A study which is undertaken after the patients have been enrolled and using data on events of interest which have already occurred. Epidemiological studies are generally of this type (see Case-control study). Risk Risk may be defined as the probability of an adverse event multiplied by the severity of the loss which experiencing that event would entail. More generally, the risk of an event is simply defined as the probability of that event occurring following exposure to the risk factor. The absolute risk is given by the incidence of the event. Therefore it requires both a numerator and denominator to calculate and is quantified on a probability scale (0 to 1). If we administer a particular antidiabetic agent to, say, 100 patients and observe that five develop diarrhoea, then an estimate of the risk of diarrhoea developing is given by 5/100 or 0.05.
142 Dictionary of Evidence-based Medicine Risk can also be expressed as a conditional probability. For example, the risk of cervical cancer (CC) in women receiving unopposed hormonal replacement therapy (HRT) can be written as P(CC|HRT) = p where p is the incidence of CC in this group of patients. Risk can be expressed in relative terms, for example risk of developing a particular adverse event among individuals exposed to a drug compared to those not exposed. If the risk (or incidence) of the event in those exposed is Re and that in the non-exposed group is Ro, the ratio (Re:Ro) is known as the risk ratio or relative risk (RR). Suppose that there are n individuals in a comparative trial of two treatments A and B and that the outcomes with respect to an adverse event are as shown in Table 7 with all the tabular entries as integers. Table 7 Calculation of relative risk from data in a contingency table Treatment A Treatment B Total Adverse event present a c a+c Adverse event absent b d b+d Total a+b c+d a+b+c+d = n The relative risk (RR) or risk ratio of the event occurring with treatment A relative to B is given by: An RR value of 5 means that the event is five times more likely to occur in the exposed group than in the non-exposed group. In pharmacoepidemiological studies investigating association between an adverse reaction and a drug, for example, the larger the RR value, the stronger the association. Values close to unity suggest no relationship and negative values suggest a negative or protective effect (e.g. intake of foods high in antioxidant compounds and cardiovascular disease). RR can only be calculated in a cohort or experimental study. The risk difference (RD) or risk reduction is given by: (see under Risk reduction).
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Dictionary of Evidence-based Medici
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Preface This book was conceived at
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A Ability to pay Ability to pay is
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Figure I Audit: Clinical audit cycl
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B Balanced design In an experiment,
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Figure 9 Concept of externality Dic
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G Game theory Game theory, first de
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I ICD (see International Classifica
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K Keynes, John Maynard (1883-1946)
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Page 100 and 101: M Macroeconomics Macroeconomics is
Page 112 and 113: N N of I trial An N of 1 trial is a
Page 116 and 117: o OBM (see Opinion-based medicine)
Page 140 and 141: Figure 25 Measuring quality of life
Page 150 and 151: S Scarcity Scarcity is often referr
Page 158 and 159: T TDM (see Therapeutic drug monitor
Page 162 and 163: u Unique value effect This term is
Page 170: Z Z variate A random variable which
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