AP Statistics Chapter 4 Notes

Population

The entire group of individuals we want information about in a statistical study.

Census

A collection of data from every individual in the population.

Sample

A subset of individuals in the population from which data is actually collected.

Bias

A design of a statistical study that consistently underestimates or overestimates the value of interest.

Convenience Sampling

A sampling method that chooses individuals easiest to reach, often leading to biased results.

Voluntary Response Sample

A sample consisting of individuals who choose themselves to respond to a general invitation, often biased.

Simple Random Sample

A sample where every set of n individuals has an equal chance of being selected.

Random Digits

A table of digits where each digit is equally likely and independent from others.

Stratified Random Sample

A sample obtained by classifying the population into strata and then taking a separate SRS from each stratum.

Cluster Sample

A sample obtained by classifying the population into clusters and then taking a SRS of the clusters.

Undercoverage

Occurs when some members of the population cannot be chosen in a sample.

Nonresponse

Occurs when an individual selected for the sample cannot be contacted or refuses to participate.

Response Bias

A systematic pattern of incorrect responses in a sample survey.

Wording Effect

Influence of question wording on survey responses.

Observational Study

A study that observes individuals and measures variables without influencing the responses.

Experiment

A study that deliberately imposes treatments on individuals to measure their responses.

Confounding

Occurs when two variables are associated in a way that their effects on a response cannot be distinguished.

Treatment

A specific condition applied to individuals in an experiment.

Experimental Units

The smallest collection of individuals to which treatments are applied.

Comparison (Experimental Design Principle)

Using a design that compares two or more treatments.

Random Assignment

Using chance to assign experimental units to treatments to create roughly equivalent groups.

Control (Experimental Design Principle)

Keeping other variables that might affect the response the same for all groups.

Replication

Using enough experimental units in each group to distinguish treatment effects from chance differences.

Statistical Significance

An observed effect so large that it would rarely occur by chance.

Completely Randomized Design

Treatment assignment to experimental units done completely by chance.

Placebo Effect

The response to an inactive treatment or a baseline treatment.

Double-Blind Experiment

Neither subjects nor those measuring response know which treatment the subject received.

Block Design

A group of experimental units known to be similar before the experiment that affects the response.

Randomized Block Design

Random assignment of experimental units to treatments within each block.

Matched Pairs Design

A randomized blocked experiment where each block consists of a matching pair of similar experimental units.