Applied Statistics Chapter 7

central limit theorem (CLT)

The CLT states that the sum or mean of a large number of independent observations from the same underlying distribution has an approximate normal distribution. The approximation steadily improves as the number of observations increases.

cluster sample

formed when the population is divided into groups (clusters) based on geographic areas

stratified random sample

formed when the population is divided into groups (strata) based on one or more classification criteria

statistical quality control

statistical techniques used to develop and maintain a firm's ability to produce high-quality goods and services

standard error

the standard deviation of an estimator

bias

the tendency of a sample statistic to systematically overestimate or underestimate a population parameter

statistic

A calculated numerical value (such as the sample mean) that characterizes some aspect of a sample set of data, and that is often meant to estimate the true value of a corresponding parameter (such as the population mean) in an underlying population; any function of a number of random variables, usually identically distributed, that may be used to estimate a population parameter

control chart

A plot of statistics of a production process over time. If the statistics randomly fall in an expected range, then the production process is in control. If the statistics reveal an undesirable trend, then adjustment of the production process is likely necessary.

parameter

A quantity or statistical measure that, for a given population is fixed and that is used as the value of a variable in some general distribution or frequency function to make it descriptive of that population: the mean and variance of a population are population parameters

simple random sample

A sample of n observations that has the same probability of being selected as any other sample of n observations. Most statistical methods presume simple random samples

random variable

a function that assigns numerical values to the outcomes of an experiment

estimate

a particular value of an estimator

estimator

a statistic used to estimate a population parameter

nonresponse bias

a systematic difference in preferences between respondents and nonrespondents of a survey or a poll

selection bias

a systematic underrepresentation of certain groups from consideration for a sample

expected value

a weighted average of all possible values of a random variable