Clinical Trials

❘❙❚■ Chapter 24 | Regression AnalysisTable 4. Assumptions and interpretations of multiple regression models.Description Linear regression Logistic regression Hazards regressionOutcome variableType Continuous Binary Time to eventDistribution Normal Bernoulli Depends on the modelCensored Not allowed Not allowed AllowedStatistic being modeled The mean value of The log of the odds The log of the hazardthe outcome variable of the outcome of the outcomePredictor variablesContinuous (x k) b kis the change in b kis the change in b kis the change inthe mean value of the the log odds of the the log hazard of theoutcome associated with outcome associated with outcome associated witha one-unit change in x ka one-unit change in x ka one-unit change in x kBinary (x k) b kis the difference in the b kis the difference in the b kis the difference in themean value of the outcome log odds of the outcome log hazard of the outcomebetween two groups between two groups; between two groups;exp(b k) is the odds ratio exp(b k) is the hazard ratiofor group 1 relative for group 1 relativeto group 0 to group 0Category (x k) b kis the difference in the b kis the difference in the b kis the difference in themean value of the outcome log odds of the outcome log hazard of the outcomebetween a group and the between a group and between a group andreference group the reference group; the reference group;exp(b k) is the odds ratio exp(b k) is the hazard ratiocomparing a group and comparing a group andthe reference group the reference groupclinical indications and performed an electron-beam tomographic scan in allpatients. Total per-patient calcium scores and separate scores for the majorcoronary arteries were added to logistic regression models to calculate aprobability of CAD, adjusting for age and gender. The ability of coronary calciumto predict obstructive disease on angiography had an overall sensitivity of 95%and specificity of 66%.With calcium scores >20, >80, and >100, the sensitivity to predict stenosisdecreased to 90%, 79%, and 76%, whereas the specificity increased to 58%, 72%,and 75%, respectively. The logistic regression model exhibited excellentdiscrimination (receiver operating characteristic curve area, 0.842 ± 0.023) andcalibration. The study concluded that electron-beam tomographic calciumscanningprovides incremental and independent power in predicting the severityand extent of angiographically significant CAD in symptomatic patients.284