In spite of this, it is assumed that a unique probability, a true risk, of an undesirable outcome for an individual exists. However, an individual either does or does not experience an undesirable outcome, so risk can never be determined for an individual. Individual risk is the probability an individual will experience an undesirable outcome. Risk is the probability of an undesirable outcome. The discordance depicted by Lemeshow and colleagues did not reflect differences in accuracy or discrimination. It makes little sense to evaluate discordance when models are inaccurate. Thus, accuracy and discrimination need to be assessed to interpret discordance. The different assignments are often interpreted as evidence that one model is superior, rather than that different predictors give different predictions.ĭiscordance can be produced by differences in accuracy or discrimination. When the predictions are discordant, individuals will be assigned to different categories by the different methods. In this approach, 2 predictive models are compared after separating patients into risk categories considered clinically important and cross‐tabulating the results for the 2 models. More recently, understanding the discordance of individual risk estimates has become important for interpreting reclassification analysis. Reproduced with kind permission from Lemeshow et al. Scatterplot of probability of hospital mortality from APACHEII and MPMII 24. During the past 40 years, individual risk estimation has been broadly accepted in medicine. An epidemiologic research method associating risk with specific risk factors in populations became a clinical method providing risk estimates for individuals. They are accurate estimates of group experience but not necessarily the experience of any individual.” The publication of this handbook represents an historic bench‐to‐bedside transition. It contained a caution: “The figures given in the tables should be taken only as guides to risk. It stated: “The purpose of this Handbook is to provide the physician with a method for easily estimating risk of coronary heart disease in patients who have no clinical evidence of coronary heart disease, and for guiding his choice of preventive management.” The handbook included tables that presented the 6‐year risk of coronary heart disease for individuals based on their risk factors. Based on this model, the American Heart Association published the Coronary Risk Handbook: Estimating Risk of Coronary Heart Disease in Daily Practice. ![]() Logistic regression was developed to analyze the epidemiologic data from Framingham.īy 1973, the logistic regression model included sex, age, cigarette smoking, blood pressure, serum cholesterol, glucose tolerance, and electrocardiography (left ventricular hypertrophy). The Framingham Heart Study played a key role in identifying risk factors for coronary artery disease, and Framingham investigators coined the term factors of risk. An example would be utilizing an individual’s blood pressure as the primary determinant of hypertension treatment decisions, not an unreliable individual risk estimate. Instead, Feinstein proposed relying on clinically important subgroups. The number calculated for an individual should not be reported as their individual or true risk, nor should it be used as the sole criterion for clinical decisions. Models relate risk factors to outcomes in populations. This issue was identified by John Venn in 1866 and is known as the reference class problem. That each of these groups may have different risk means there is no such thing as individual risk. Many groups, like any individual, can be identified, eg, groups of the same age, sex, race, or any combination of these attributes (or any others). Groups of like individuals need to be assembled to measure the probability of an outcome. This lack of reliability is an inherent limitation and is not resolved by including additional risk factors. Outside Mendelian inheritance, risks are conditional probabilities and differ as the risk factors included differ, at times substantially. ![]() Patients don’t have an “individual risk” or unique probability of an outcome.
0 Comments
Leave a Reply. |