Section 4.1 (AP Statistics)

population

In a statistical study, the entire group of individuals about which we want information.

sample

The part of the population from which we actually collect information. We use information we collected to draw conclusions about the entire group.

sample survey

A study that uses an organized plan to choose a sample that represents some specific population. We base conclusions about the population on data from it.

convenience sample

A sample selected by taking the members of the population that are easiest to reach; particularly prone to large bias.

bias

The design of a statistical study shows bias if it systematically favors certain outcomes.

voluntary response sample

People decide whether to join a sample based on an open invitation; particularly prone to large bias because people with strong opinions (often in the same direction) are most likely to respond.

random sampling

The key technique employed by survey researchers, which operates on the principle that everyone should have an equal probability of being selected for the sample.

Simple Random Sample (SRS)

A sample where n individuals from the population are chosen in such a way that every set of n individuals has an equal chance to be the sample actually selected.

table of random digits

A long string of the digits 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 with these properties:

• Each entry is equally likely to be any of the 10 digits 0 through 9.

• The entries are independent of each other. That is, knowledge of one part of the table gives no information about any other part.

stratified random sample

To select a stratified random sample, first classify the population into groups of similar individuals, called strata. Then choose a separate SRS from each stratum to form the full sample.

cluster sample

Is obtained by selecting all individuals within a randomly selected collection or group of individuals.

Inference

Drawing conclusions that go beyond the data at hand.

margin of error

Tells how close the estimate tends to be to the unknown parameter in repeated random sampling.

sampling frame

The list from which a sample is actually chosen.

sampling error

A statistical error that occurs when an analyst does not select a sample that represents the entire population of data. The results found in the sample thus do not represent the results that would be obtained from the entire population.

nonsampling error

Refers to an error that results during data collection, causing the data to differ from the true values. It is the most serious errors in most careful surveys. These have nothing to do with choosing a sample—they are present even in a census.

undercoverage

A kind of sampling error that occurs when some members of the population are left out of the sampling frame.

nonresponse

A nonsampling error that occurs when a selected individual cannot be contacted or refuses to cooperate.

response bias

A systemic pattern of incorrect responses.

wording of questions

The most important influence on the answers given to a survey. Confusing or leading questions can introduce strong bias, and changes in wording can greatly change a survey's outcome. Even the order in which questions are asked matters.