Small Clinical Trials Issues and Challenges (2001) / Chapter Skim
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Appendix B Glossary of Statistical and Clinical Trials Terms
Appendix B Glossary of Statistical and Clinical Trials Terms
Pages 130-176
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arc! Clinical Trials Terms Acceptance region The set of values of a test statistic for which the null hypothesis is not rejected.
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Alternative hypothesis The hypothesis against which the null hypothesis is testecl. Analysis of covariance (ANCOVA)
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Association Statistical dependence between two or more events, characteristics, or other variables. Most often applied in the context of binary variables forming a two-by-two contingency table.
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The process clears with probabilities of hypotheses and probability distributions of parameters, which are not taken into account in classical statistical inference. Bayes's theorem A theorem in probability theory named after Thomas Bayes (1702-1761)
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Data involving this type of variable often require specialized statistical techniques such as logistic regression. Binomial distribution The probability distribution of the number of occurrences of a binary event in a sample of n independent observations.
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The Western blot is widely used in a test for detection of human immunodeficiency virus infection. Bootstrap A data-based simulation method for statistical inference that can be used to study the variability of estimated characteristics of the probability distribution of a set of observations and provide confidence intervals for parameters in situations in which these are difficult or impossible to derive in the usual way.
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Chimerism In genetics, the presence in an individual of cells of different origin, such as of blood cells derived from a dizygotic cotwin. Chi-square distribution The probability distribution of the sum of squares of a number of independent standard normal variables.
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Clinical trials have four phases: Phase I Safety ancl pharmacologic profiles. This involves the initial introcluction of a candidate vaccine or drug into a human population to determine its safety ancl mode of action.
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or joint probability distributions (in a Bayesian application) for parameters of interest.
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Control group Subjects with whom comparison is made in a case-control study, randomized controlled trial, or some other variety of epiaemiological study. Controlled trial A phase III clinical trial in which an experimental treatment is compared with a control treatment, the latter being either the current standard treatment or a placebo.
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Critical region The values of a test statistic that lead to rejection of a null hypothesis. The size of the critical region is the probability of obtaining an outcome belonging to this region when the null hypothesis is true, i.e., the probability of a Type I error.
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Examples include normal distribution, lognormal distribution, chi-square distribution, ~ distribution, F distribution, and binomial distribution. Dose-ranging trial A clinical trial, usually undertaken at a late stage in the development of a drug, to obtain information about the appropriate
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The error of rejecting a true null hypothesis, i.e., declaring that a difference exists when it does not.
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If a single figure for the unknown parameter is calculatecl, the process is called "point estimation." If an interval within which the parameter is likely to fall is calculatecl, the procedure is called "interval estimation." Exact method A statistical method based on the actual, i.e., "exact," probability distribution of the study data rather than on an approximation such as the normal or chi-square clistribution, e.g., Fisher's exact test. Experimental study A study in which conditions are under the direct control of the investigator.
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Fitted value Refers to the value of the response variable predicted by some estimated model. Five-number summary A method of summarizing a set of observations by using the minimum value, the lower quartile, the median, upper quartile, and maximum value.
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The other components of such models are a specification of the form of the variance of the response variable and of its probability distribution. Goodness-of-fit Degree of agreement between an empirically observed distribution and a mathematical or rhetorical distribution.
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Antigens on cell surfaces that are important for foreign antigen recognition and that play a role in the coordination and activation of the immune response. Hypergeometric distribution The exact probability distribution of the frequencies in a two-by-two contingency table, conditional on the marginal frequencies being fixed at their observed levels.
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Informative censoring Censored observations that occur for reasons related to treatment, e.g., when treatment is withdrawn as a result of a deterioration in the physical condition of a patient. Informative prior A term used in the context of Bayesian inference to indicate a prior distribution that reflects empirical or theoretical information regarding the value of an unknown parameter.
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Also used to describe investigation of a single subject. See e-of-1 clinical trials.
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Kurtosis The extent to which the peak of a unimodal probability distribution or frequency distribution departs from the shape of a normal distribution by either being more pointed (leptokurtic) or flatter (platykurtic)
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Log-normal distribution The probability distribution of a variable, x, for which log (x - a) has a normal distribution with mean m and variance 62e Log-rank test A method for comparing the survival times of two or more groups of subjects that involves the calculation of observed and expected frequencies of failures in separate time intervals.
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Mantel-Hacnszel estimate An estimate of the assumed common odds ratio in a series of two-by-two contingency tables arising from different populations, e.g., occupation or country of origin. Mantel-Hacnszel test A calculated test statistic that uses a standard normal deviate rather than a chi-square value.
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Minimization A method for allocation of patients to treatments in clinical trials that is usually an acceptable alternative to random allocation. The procedure ensures balance between the groups to be compared on prognostic variables, by allocating with a high degree of probability the next patient to enter the trial to whatever treatment would minimize the overall imbalance between the groups on the prognostic variables, at that stage of the trial.
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Multicenter study A clinical trial conducted simultaneously in a number of participating hospitals or clinics, with all centers following a universal study protocol and with independent random allocation within each center. Multicollinearity In multiple regression analysis, a situation in which at least some of the independent variables are highly correlated directly or indirectly with each other.
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Multivariate data Data for which each observation consists of values for more than one random variable, e.g., measurements of blood pressure, temperature, and heart rate for a number of subjects. Multivariate distribution The simultaneous probability distribution of a set of random variables.
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The term p represents the probability of a "success" of any trial. Normal distribution A probability distribution of a random variable, x, that is assumed by many statistical methods.
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Increasing the number of controls beyond 5 to 10 brings rapidly diminishing returns. One-tailed test A statistical significance test based on the assumption that the data have only one possible direction of variability.
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Parallelism in analysis of covariance One of the assumptions made in the analysis of covariance, namely, that the slope of the regression line relating the response variable to the covariate is the same in all treatment groups. Parametric hypothesis A hypothesis concerning the parameters of a distribution, e.g., the hypothesis that the mean for a population equals the mean for a second population when the populations are each assumed to have a normal distribution.
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Placebo reactor A term for those patients in a clinical trial who report side effects normally associated with the active treatment while receiving a placebo. Play-the-winner rule A procedure in clinical trials in which the response to treatment is either positive (a success)
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Prior distribution Probability distribution that summarizes information about a random variable or parameter known or assumed at a given time point before further information about empirical data is obtained. It is used in the context of Bayesian inference.
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For example, in investigating the assumption that a set of data is from a normal distribution, the ordered sample values, X`1', X`2',.
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Quantit model A three-parameter nonlinear logistic regression model. Quartiles The values that divide a frequency distribution or probability distribution into four equal parts.
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Random variable A variable, the values of which occur according to some specified probability distribution. Random variation The variation in a data set unexplained by identifiable sources.
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Regression analysis A general term for methods of analysis that are concerned with estimating the parameters in some postulated relationship between a response variable and one or more explanatory variables. Examples are linear regression, logistic regression, and multiple regression.
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Response variable The variable of primary importance in medical investigations, since the major objective is usually to study the effects of a treatment or other explanatory variables on this variable. Restricted maximum likelihood estimation (REML)
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It takes into account the incidence or prevalence of the condition being studied, the estimated or putative relationship among the variables in the study, the power that is desired, and the allowable Type I error. Sampling distribution The probability distribution of a statistic.
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Sequential analysis A method of analysis in which a statistical test of significance is conducted repeatedly over time as the data are collected. After each observation, the cumulative data are analyzed and one of the following three decisions is taken: · stop the data collection, reject the null hypothesis, and claim sta.
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Singly censored data Censored observations that occur in clinical trials in which all the patients enter the study at the same time point and in which the study is terminated after a fixed time period. Skewness The lack of symmetry in a probability distribution.
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Statistical significance An estimate of the probability of the observed or greater degree of association between independent and dependent variables under the null hypothesis. The level of statistical significance is usually stated by the p value.
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Structural zeros Zero frequencies occurring in the cells of contingency tables that arise because it is theoretically impossible for an observation to fall in the cell. Student's t distribution The probability distribution of the ratio of a standard normal variable to the square root of a variable with a chi-square distribution.
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t distribution The distribution of a quotient of independent random variables, the numerator of which is a standardized normal variate and the denominator of which is the positive square root of the quotient of a chi-square-distributed variate and its number of degrees of freedom. Test statistic A statistic used to assess a particular hypothesis in relation to some population.
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than a fixed value are either not recorded or not observed. t test Test that uses a statistic that, under the null hypothesis, has the distribution to test whether two means differ significantly or to test lin.
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Unbiased estimator An estimator that for all sample sizes has an expected value equal to the parameter being estimated. If an estimator tends to be unbiased as the sample size increases, it is referred to as "asymptotically unbiased." Uniform distribution The probability distribution of a random variable having constant probability over an interval.
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In the case of a balanced design, estimation of these variances is usually achieved directly from the appropriate analysis of variance table by equating mean squares to their expected values. When the data are unbalanced, a variety of estimation methods might be used, although maximum likelihood estimation and restricted maximum likelihood estimation are most often used.
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Volunteer bias A possible source of bias in clinical trials involving volunteers, but not involving random allocation, because of the known propensity of volunteers to respond better to treatment than other patients. Wald's test A test for the hypothesis that a vector of parameters, 0' = I 01' 02' .
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z test A test for assessing hypotheses about population means when their variances are known. If the null hypothesis is true, z has a standard normal distribution.
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1992. Meta-Analysis by the Confidence Profile Method.
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Key Terms
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