Clinical Trials

❘❙❚■ GlossaryPer-protocol analysisA method of analysis in which only the subset of subjects who compliedsufficiently with the protocol are included. Protocol compliance includes exposureto treatment, availability of measurements, correct eligibility, and absence of anyother major protocol violations. This approach contrasts with the moreconservative and widely accepted ‘intention-to-treat’ analysis.PowerThe probability of rejecting the null hypothesis (eg, no treatment difference)when it is false. It is the basis of procedures for calculating the sample sizerequired to detect an expected treatment effect of a particular magnitude.Random errorAn unpredictable deviation of an observed value from a true value resulting fromsampling variability. It is a reflection of the fact that the sample is smaller than thepopulation; for larger samples, the random error is smaller, as opposed to systematicerrors (bias) that keep adding up because they all go in the same direction.Regression analysesMethods of explaining or predicting outcome variables using information fromexplanatory variables. Regression analyses are often used in clinical trials toestimate the adjusted treatment effect taking into account differences in baselinecharacteristics, and in epidemiological studies to identify prognostic factors whilecontrolling for potential confounders. Commonly used regression models includelinear, logistic, and Cox regression methods.Risk factorA risk factor can be defined as anything in the environment, personal characteristics,or events that make it more or less likely one might develop a given disease,reach an adverse event, or experience a change in health status. For example,raised cholesterol is a risk factor for heart attacks.458