Dictionary of Evidence-based Medicine.pdf

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Dictionary of Evidence-based Medicine 149 Standardized mortality rate The standardized mortality rate is a mortality rate adjusted to take account of the composition of the population to which it refers. Standards of quality Standards of quality are authoritative statements of (i) minimum levels of acceptable performance or results; (ii) excellent levels of performance or results; (iii) the range of acceptable performance or results (Field MJ, Lohr KN (eds) (1990) Clinical practice guidelines: directions for a new program. National Academy Press, Washington DC). STAR-PUs When undertaking comparisons of prescribing trends across different regions of a country, simple averages and proportions can be highly misleading because it is well known that the elderly, for example, require medication more frequently than the young. Therefore, doctors serving areas with a higher proportion of elderly patients would be expected to prescribe more. The STAR-PU (or specific therapeutic group age-sex related prescribing unit) is a weighting scheme developed to make some of the necessary adjustments before cost comparisons are made at the therapeutic group level (see ASTRO-PUs. Lloyd DCEF, Harris CM, Roberts DJ (1995) Specific therapeutic age-sex related prescribing units (STAR-PUs): weightings for analysing general practices' prescribing in England. BMJ. 311: 991-4). State-transition model The state-transition model is a dynamic mathematical model which assigns individuals from a population to different categories or health states at recurring time intervals with defined transition probabilities. The model is often used to obtain estimates of life expectancy or quality-adjusted life expectancy. A state-transition model which assumes that the transition probabilities are dependent only on the current state is called a Markov model (Krahn MD, Mahoney MH, Eckman J et al. (1994) Screening for prostate cancer. A decision-analytic view. Journal of the American Medical Association. 272: 273-80). Stochastic model A stochastic model is one which uses randomly generated data or parameters from particular probability distributions to describe a system,
150 Dictionary of Evidence-based Medicine usually for predictive purposes. For example, in modelling patient throughput at a hospital pharmacy or clinic, the build-up of queues may be stochastically modelled by a computer simulating the arrival of patients by sampling from a Poisson distribution and the service time by sampling from an exponential distribution. Such a model can be used, for example, to predict the number of servers which would be required based on what would be judged to be acceptable waiting times. With computers, it is relatively easy to simulate even highly complex events such as the time spent by a cohort of patients in different health states (see State-transition model). In contrast, models which do not take account of the randomness of data and/or parameters by simulation are called deterministic models. These may be based on simple algebraic formulae such as number of servers required equals average number of patients arriving during the day divided by average number of patients which one pharmacist or doctor can attend to. Alternatively, differential equations may be used to describe the system being modelled. Such deterministic models are often used in pharmacokinetic studies although stochastic modelling is being increasingly used too, particularly when making predictions about individuals from population data. Note that precision estimates can still be made for predictions based on deterministic models provided we are willing to make assumptions about the precision or probability distribution of the input data. Studentized value A value which has been standardized by dividing it with its associated error to yield a dimensionless score. Thus the standardized residual is the residual divided by the estimated standard deviation of that residual. Subjective preference In the context of clinical trials or choice of treatment, subjective preference describes the choice of a particular treatment based on hunch, advice from friends or relatives or similar types of information. This is to be contrasted with informed choice when patients base their preferences on reliable estimates of risks and benefits from reliable data such as those derived from robust clinical trials or systematic overviews. However, irrespective of which approach is used, patients' preferences are often highly variable particularly when there are (i) major differences in possible outcomes; (ii) major differences between treatments in the range, likelihood and severity of outcomes; (iii) choices involving trade-offs between short- and long-term outcomes; (iv) choices involving a small probability of a major
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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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M Macroeconomics Macroeconomics is
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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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