# Vocab #8

## 18 terms

### 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=xbar-mu/x/√n

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