AP Stats Chapter 4: Sampling, Surveys, and Experiments

Flashcards covering sampling methods, experimental design principles, biases, and scope of inference from AP Stats Sections 4.1, 4.2, and 4.3 notes by Charlotte Foreman.

Population

The entire group you're interested in for a statistical study.

Sample

The part of the population from which you actually collect data.

Simple Random Sample (SRS)

A subset of individuals from the population where every possible group of $n$ individuals has an equal chance of being selected.

Stratified Random Sample

Method where the population is divided into strata (groups of similar individuals) and a separate SRS is selected from each stratum.

Cluster Sample

Method where the population is divided into clusters (usually by location), some clusters are randomly selected, and every individual within those clusters is included in the sample.

Systematic Random Sample

A methodology where researchers randomly choose a starting point and select every $k\text{-th}$ individual after that.

Undercoverage

A potential bias that occurs when some groups of the population are left out of the selection process.

Nonresponse

A source of bias when individuals selected for the sample cannot be contacted or choose not to respond.

Response Bias

A bias that occurs when people may lie or give inaccurate answers, often influenced by wording or the interviewer.

Wording of Questions

A potential source of bias where poorly worded or leading questions influence responses.

Census

A collection of data from every individual in the population.

Sampling Frame

The list of individuals from which the sample is actually chosen.

Voluntary Response Sampling

A bad sampling method where people choose to respond themselves, typically attracting those with strong opinions.

Convenience Sampling

A sampling method where individuals are chosen because they are easy to reach, such as friends or people in a hallway.

Experimental Units

The individuals (people, animals, objects) on which the experiment is done.

Subjects

The term used for experimental units when they are people.

Treatment

A specific condition applied to the units in an experiment.

Factor

An explanatory variable that is manipulated by the researcher.

Level

Specific values of a factor in an experiment.

Response Variable

The outcome measured in an experiment.

Comparison

An experimental design principle that involves using two or more treatment groups.

Random Assignment

The use of chance to assign experimental units to treatments to help balance out unknown or uncontrollable variables.

Control

The principle of keeping other variables constant to avoid confounding.

Replication

The use of enough subjects to ensure that results are reliable and not due to chance.

Confounding

Occurs when the effects of two variables on the response variable cannot be distinguished from one another.

Completely Randomized Design (CRD)

A design where all units are randomly assigned to treatments with no grouping beforehand.

Randomized Block Design (RBD)

A design where units are first grouped into blocks of similar individuals, then randomized to treatments within each block.

Matched Pairs Design

A type of block design where subjects are either paired by similarities or the same individual receives both treatments in a random order.

Placebo

A fake treatment used in experiments that has no active ingredient.

Single-blind

A design where either the subjects or the experimenters do not know which treatment was given.

Double-blind

A design where both the subjects and those interacting with them are unaware of which treatment assignment was given.

Statistically Significant

An observed effect that is unlikely to occur by chance alone in a simulation or random assignment.

Scope of Inference

The limit of a study's conclusions; generalization to a population requires random sampling, while establishing cause-and-effect requires random assignment.

Observational Study

A study that observes individuals and measures variables of interest without attempting to influence responses or imposing treatments.