AP Stats Unit 3

Simple random sample

Every individual has an equal chance at being selected, least variation, every combo is equally likely, RNG

Stratified random sample

Divide pop into groups based on similarity, homogenous, each strata is random, least variation, everyone is represented

Cluster sample

Heterogenous cluster, group-cluster, pop divided into clusters and survey everyone in that group, more variation

Systemic random sample

Put pop in random orders, choose starting point, select every kth individual, most variation

Convenience random sample

Pick who is easily available, more variation

Voluntary sample

An easy, cheap, and biased survey where individuals choose to participate, more variation

Under coverage

Some individuals are less likely to be chosen ( left out / no chance )

Nonresponse

Individual can't be reached or won't respond

Response bias

Self-reporting, wording of the question

Population

Entire group of interest, parameters

Sample

Subset of population, statistics

Groups

Strata

Causation

Needs an experiment

Experiment

Treatment is being imposed, randomly assigned treatment, causation

Observational study

Data collected from random sample, can generalize to population

Treatment

What is done ( or not ) to the experimental units

Experimental units

Who / what gets the treatment

Confounding variables

Outside variables

Blinding

Unit doesn't know