Clinical Trials

Clinical Trials: A Practical Guide ■❚❙❘Standard errorA measure of the random variability of a statistic (eg, mean, proportion, treatmenteffect) indicating how far the statistic is likely to be from its true value.For example, standard error of the mean (SEM) indicates uncertainty of a singlesample mean (X) as an estimate of the population mean (μ). A smaller SEMimplies a more reliable estimate of the population mean. Standard error can beused to calculate a confidence interval of an estimated population parameter.The smaller the standard error, the narrower the confidence interval, and themore precise the point estimate of the population parameter.Treatment effectAn effect attributed to a treatment in a clinical trial, often measured as thedifference in a summary measure of an outcome variable between treatmentgroups. Commonly expressed as a difference in means for a continuous outcome,a risk difference, risk ratio, or odds ratio for a binary outcome, and a hazard ratiofor a time-to-event outcome.Univariate/multivariate analysisThe term variate refers to the term variable. A univariate analysis examines theassociation between a single variable and an outcome variable (correctly calleda bivariate analysis), for example, age and occurrence of stroke. In a multivariateanalysis, associations between many variables are examined simultaneously.In particular, multivariate regression analysis can be used to assess the relativeimportance and contribution of each predictor variable to the outcome variable.For example, a multivariate logistic regression can be undertaken to identify themost important prognostic factors among several risk factors (eg, age, sex, systolicblood pressure, and cholesterol level) that predict the occurrence of stroke.459