Treatment and control groups - Treatment and control groups are comparison groups used to assess an intervention.
Trend-stationary process - A trend-stationary process is a time series that becomes stationary after removing a deterministic trend.
Trimmed samples - Trimmed samples are samples from which a specified portion of the most extreme observations has been excluded for a particular analysis.
Trimmed statistics - Trimmed statistics are numerical summaries calculated after excluding a specified portion of extreme observations.
Truncated normal distribution - A truncated normal distribution is the distribution of a normally distributed variable conditional on its value lying within specified bounds.
Tukey - Duckworth test - The Tukey-Duckworth test is a simple two-sample test that uses counts of nonoverlapping observations at opposite ends of the combined data.
Tukey's B method - Tukey's B method is a multiple-comparison procedure for comparing group means that combines features of Tukey's honestly significant difference procedure...
Tukey's HSD test - Tukey's HSD test, short for honestly significant difference, is a procedure for comparing every pair of group means while controlling the familywise...
Tukey's range test - Tukey's range test is a common name for Tukey's honestly significant difference procedure, which compares group means using the studentized range distribution.
Tukey's test of additivity - Tukey's test of additivity is a one-degree-of-freedom test for a particular form of nonadditivity in a two-way layout.
Tukey's trend test - Tukey's trend test is an approach to detecting a dose-response trend by examining regression slopes under several prespecified dose scales, commonly...
Two-proportion Z-test - A two-proportion Z-test is a large-sample hypothesis test comparing two independent population proportions.
Two-sample hypothesis testing - Two-sample hypothesis testing uses observations from two samples to assess a specified claim about their source populations or distributions.
Two-sided test - A two-sided test evaluates departures from a null hypothesis in either direction.
Twoway factorial design - A two-way factorial design studies two factors by including every combination of their selected levels.
Type I error - A Type I error occurs when a statistical hypothesis test rejects a null hypothesis that is true.
Type II error - A Type II error occurs when a statistical test fails to reject a null hypothesis that is false.
Type III error - Type III error is a statistical expression with several meanings, so its intended definition must be stated.
Ultimate sampling unit - An ultimate sampling unit is a unit selected at the final stage of a sampling design.
Uncomfortable science - Uncomfortable science is an informal methodological expression for research situations where limited available evidence is used both to develop explanations...
Unconditional probability - Unconditional probability is the probability of an event without restricting the calculation to a specified conditioning event.
Unevenly spaced time series - An unevenly spaced time series is a sequence of observations recorded at times whose successive gaps are not all equal.
Uniform distribution - A uniform distribution assigns equal probability to outcomes of equal size within its support.
Uniform sampling fraction - A uniform sampling fraction means that the same proportion of units is selected from each stratum of a stratified population.
Uniformly most powerful test - A uniformly most powerful test is a hypothesis test whose power is at least as high as that of every competing test in a specified class, at every parameter...
Unimodal - Unimodal describes a distribution or data pattern with one mode, commonly understood as one principal peak.
Unit Gompertz distribution - The unit Gompertz distribution is a continuous probability distribution on the open interval from zero to one, constructed by an exponential transformation...
Unit Weibull distribution - The unit Weibull distribution is a continuous distribution on the open interval from zero to one, obtained by transforming a positive Weibull variable with...
Unit-weighted regression - Unit-weighted regression is a simple linear prediction approach that combines predictors using equal-magnitude weights, commonly after standardizing them...
Univariate design - A univariate design is an experimental design with one dependent variable or outcome.
Unmatched count - Unmatched count refers to an indirect survey technique, also called the item count technique or list experiment, for estimating the prevalence of a...
Unobserved heterogeneity in duration models - Unobserved heterogeneity in duration models means that units differ in their tendency to experience an event for reasons not captured by the observed...
Up-and-down design - An up-and-down design is a sequential experimental design in which the level used for the next observation depends on the preceding response.
Uplift modeling - Uplift modeling estimates how an intervention changes an outcome, often as a function of a person's or item's characteristics.
Upper confidence bound - An upper confidence bound is an upper limit intended to cover an unknown quantity with a specified confidence under stated assumptions.
Van der Waerden test - The Van der Waerden test is a rank-based test that compares independent groups by converting pooled ranks into standard normal quantiles, called normal scores.
Variable sampling fraction - A variable sampling fraction means that different proportions of units are selected from different parts of a population, commonly from different strata.
Variables sampling plan - A variables sampling plan is an acceptance-sampling procedure that uses quantitative measurements from sampled items to decide whether to accept a lot.
Variance - Variance measures spread by averaging squared deviations from a mean.
Variance components - Variance components are parameters that represent distinct sources of random variation in a statistical model.
Variance estimation - Variance estimation is the task of estimating the variability of a statistical estimator across repeated samples or repeated realizations of its...
Variance inflation factor ( VIF ) - The variance inflation factor, or VIF, measures how linear relationships among predictors inflate the variance of an estimated ordinary least squares...
Variance Sum Law - The variance sum law gives the variance of a sum or difference of random variables, including their covariance.
Variational Bayesian methods - Variational Bayesian methods approximate a Bayesian posterior by choosing a tractable probability distribution from a specified family and optimizing it to...
Vecchia approximation - The Vecchia approximation is a way to approximate a large joint probability distribution, especially a Gaussian process, by multiplying conditional...
Venn diagrams - Venn diagrams use overlapping regions to represent sets and the possible combinations of membership among them.
Virtual sensing - Virtual sensing estimates a quantity that is difficult, costly or impractical to measure directly by using a model and other available measurements.
Vuong's closeness test - Vuong's closeness test compares statistical models by their expected log likelihood, which corresponds to relative closeness to the data-generating...