Clinical Trials

Clinical Trials: A Practical Guide ■❚❙❘Correlation coefficient (r)A measure of the linear association between two continuous variables. Thecorrelation coefficient varies between –1.0 and +1.0. The closer it is to 0, theweaker the association. When both variables go in the same direction (eg, heightand weight) r has a positive value between 0 and 1.0 depending on the strength ofthe relationship. When the variables go in opposite directions (eg, left ventricularfunction and life-span) r has a negative value between 0 and –1.0, depending onthe strength of this inverse relationship.CovariatesGenerally used as an alternative name for explanatory variables in the regressionanalysis but more specifically referring to variables that are not of primary interestin an investigation. Covariates are often measured at baseline in clinical trialsbecause it is believed that they are likely to affect the outcome variable andconsequently need to be included to estimate the adjusted treatment effect.Descriptive/inferential statisticsDescriptive statistics are used to summarize and describe data collected in a study.To summarize a quantitative (continuous) variable, measures of central location(ie, mean, median, mode) and spread (eg, range and standard deviation) are oftenused, whereas frequency distributions and percentages (proportions) are usuallyused to summarize a qualitative variable. Inferential statistics are used to makeinferences or judgments about a larger population based on the data collectedfrom a small sample drawn from the population. A key component of inferentialstatistics is hypothesis testing. Examples of inferential statistical methods are thet-test and regression analysis.EndpointA clearly defined outcome associated with an individual subject in clinicalresearch. Outcomes may be based on safety, efficacy, or other study objectives(eg, pharmacokinetic parameters). An endpoint can be quantitative (eg, systolicblood pressure, cell count), qualitative (eg, death, severity of disease), or time-toevent(eg, time to first hospitalization from randomization).455