Test statistic —
Third quartile —75th percentile
Treatment variable —see explanatory variable
Tree diagram —graphical technique for showing all possible outcomes in a probability experiment
Two-sided alternative —alternative hypothesis that can vary from the null in either direction; values
much greater than or much less than the null provide evidence against the null
Two-sided test —a hypothesis test with a two-sided alternative
Two-way table —table that lists the outcomes of two categorical variables; the values of one category
are given as the row variable, and the values of the other category are given as the column variable;
also called a contingency table
Type I error —the error made when a true null hypothesis is rejected
Type II error —the error made when a false null hypothesis is not rejected
Unbiased estimate —mean of the sampling distribution of the estimate equals the parameter being
estimated
Undercoverage —some groups in a population are not included in a sample from that population
Uniform —distribution in which all data values have the same frequency of occurrence
Univariate data —having to do with a single variable
Variance —average of the squared deviations from their mean of a set of observations;
Voluntary response bias —bias inherent when people choose to respond to a survey or poll; bias is
typically toward opinions of those who feel most strongly
Voluntary response sample —sample in which participants are free to respond or not to a survey or a
poll
Wording bias —creation of response bias attributable to the phrasing of a question
z -score —number of standard deviations a term is above or below the mean;