AP Statistics Notes: Unit 3

Population

The entire group of individuals or items being studied.

Sample

A subset of a population used to represent the whole.

Random Sampling

A sampling method that gives every individual an equal chance of being selected.

Stratified Sampling

A method where groups are created and then random samples are taken from each group.

Cluster Sampling

A method that involves dividing the population into clusters and randomly selecting entire clusters.

Bias

A systematic favoring of certain responses over others in sampling.

Undercoverage

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

Nonresponse

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

Voluntary Response Sample

A sample made up of individuals who choose themselves by responding to a general invitation.

Convenience Sample

A sample consisting of individuals who are easily reached.

Experimental Design

A plan for how to conduct an experiment to ensure valid results.

Replication

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

Control Group

The group in an experiment that does not receive the treatment and is used as a benchmark.

Observation Study

A study in which individuals are observed and measurements are taken without treatment.

Experimental Study

A study where the researcher actively manipulates variables to observe effects.

Control Group

The main purpose of a control group is to provide a baseline for comparing the effects of the other treatments.

Completely Randomized Design

An experimental design where the experimental units are assigned to treatments completely by chance.

Double-Blind Experiment

An experimental design where neither the subjects nor those measuring the response variable know which treatment a subject received.

Single-Blind Experiment

An experimental design where only the researcher knows which treatment the experimental units received.

Statistically Significant

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

Block

A group of experimental units known to be similar in some way that is expected to affect the response to treatments.

Randomized Block Design

An experimental design where random assignment to treatments is carried out separately within each block.