AP Statistics - Chapter 4

simple random sample

The sampling method where everyone has an equal chance of being picked.

convenience sample

The sampling method where individuals who are easiest to reach are picked.

bias

When a statistical study is very likely to overestimate or underestimate a value.

voluntary response sampling

Sampling method where people choose to be in the sample by responding to a general invitation.

stratified random sampling

Sampling method where an SRS is chosen for each stratum and combined into one overall sample.

strata

Groups of individuals in a population who share characteristics thought to be associated with the variable being measured in a study.

cluster

A group of individuals in the population that are near each other.

cluster sampling

Sampling method that selects a sample by randomly choosing clusters and including each member of the selected cluster in the sample.

systematic random sampling

Sampling method that selects a sample from an ordered arrangement of the population by randomly selecting one of the first k individuals and choosing every kth individual thereafter.

undercoverage

A bias where some members of the population are less likely to be chosen in the sample.

nonresponse bias

A bias that occurs when an individual cannot be contacted or refuses to participate.

response bias

A bias where there is a systematic pattern of inaccurate answers to a survey question, such as due to suggestive wording of the question.

retrospective

A type of observational study that examines existing data for a sample of individuals.

prospective

A type of observational study that tracks individuals into the future.

observational study

A study that observes individuals and measures variables of interest but does not attempt to influence the response.

response variable

A variable that measures an outcome of a study.

explanatory variable

A variable that may help explain or predict changes in a response variable.

confounding

When two variables are associated in such a way that their effects on a response variable cannot be distinguished from each other.

experiment

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

placebo

A treatment that has no active ingredients, but otherwise is like other treatments.

treatment

A specific condition applied to the individuals in an experiment.

experimental unit

the object to which a treatment is randomly assigned.

subject

An experimental unit that is a person.

factor

A variable that is manipulated and may cause change in the response variable.

level

A specific value that a factor can take.

control group

A group in an experiment used to provide a baseline for comparing the effects of other treatments.

placebo effect

The phenomenon that some subjects will respond favorably to any treatment, even an inactive treatment.

double-blind

When neither the subjects nor the researchers who interact with them know which treatment a subject received.

single-blind

Either the subjects or the people who interact with them don’t know which treatment a subject received.

random assignment

When experimental units are assigned to treatments using a chance process.

control

Keeping other variables constant for experimental units.

replication

Using enough experimental units to distinguish a difference in the effects of treatments from chance variation due to random assignment.

principles of experimental design

Comparison, random assignment, control, and replication.

completely randomized design

When experimental units are assigned to treatments completely by chance.

block

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

randomized block design

When random assignment to experimental units is carried out separately within each block.

matched pairs design

A type of randomized block design that uses block sizes of 2.

sampling variability

The fact that different samples of the same size from the same population produce different estimates.

statistically significant

When the results of a study are too unusual to be explained by chance alone.