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stratified random sample

groups of interest (strata) chosen in such a way that they appear in approximately the same proportions in the sample as in the population

subjects

human experimental units

survey

obtaining responses to questions from individuals

symmetric

data values distributed equally above and below the center of the distribution

systematic bias

the mean of the sampling distribution of a statistic does not equal the mean of the population; see unbiased estimate

systematic sample

probability sample in which one of the first n subjects is chosen at random for the sample and then each nth person after that is chosen for the sample

t distribution

the distribution with n-1 degrees of freedom for the t statistic

t statistic

t=xbar-mu/x/√n

third quartile

75th percentile

treatment variable

explains changes in response variable; treatment variable; independent 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 hypothesis is rejected

type-II error

the error made when a false hypothesis is not rejected

unbiased estimate

mean of the sampling distribution for the estimate equals the parameter being estimate

undercoverage

some groups in a population are not included in a sample from that population