AP Statistics Unit 1B Study Guide

Population

The entire group you want information about.

Sample

The individuals from whom data are actually collected.

Census

Data collected from every member of the population.

Parameter

A number describing a population.

Statistic

A number calculated from a sample; used to estimate a parameter.

Inference

Using sample results to draw a conclusion about a population.

Random sampling

Generalizing results to the population.

Random assignment

Making a cause-and-effect conclusion.

Causation question

For [population], does [explanatory variable/treatment] cause an increase or decrease in [response variable], compared with [comparison group]?

Observational study

Researchers observe or ask about variables; they do not assign treatments. Can identify associations but cannot establish causation.

Experiment

Researchers impose treatments on experimental units and measure the response.

Explanatory variable

The variable used to explain or predict changes.

Response variable

The outcome measured.

Treatment

A specific condition imposed in an experiment.

Experimental unit

The individual or object receiving a treatment. When units are people, they’re often called subjects.

Comparison

Comparing at least two treatments or a treatment with a control/placebo.

Replication

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

Control group

A comparison group that does not receive the active treatment, or receives a standard treatment.

Placebo

An inactive treatment designed to resemble the real one.

Placebo effect

A response caused by receiving a treatment or believing one was received, rather than by the active ingredient.

Blinding

Keeping participants and/or researchers unaware of treatment assignments to reduce bias.

Completely randomized design

Randomly assign all experimental units directly to treatment groups.

Randomized block design

First divide units into blocks based on a characteristic likely to affect the response. Randomly assign treatments within each block.

Matched-pairs design

A special kind of block design where similar units are paired and randomly assigned to treatments.

Simple random sample (SRS)

Every possible sample of the chosen size has an equal chance of being selected.

Stratified random sample

Divide the population into strata based on a characteristic and take an SRS from every stratum.

Cluster random sample

Divide the population into natural groups called clusters and survey everyone in randomly selected clusters.

Systematic random sample

Randomly select a starting point and select every k-th individual after that.

Undercoverage

Some population members are missing or are less likely to be selected.

Nonresponse

Selected people cannot be reached or do not respond.

Response bias

People give inaccurate answers, perhaps due to question wording, embarrassment, or pressure.

Voluntary response bias

People choose themselves whether to participate, leading to strong opinions affecting responses.

Convenience sampling

Researchers sample individuals who are easiest to reach.

Observational study conclusion wording

"There is an association between ___ and ___ among the individuals studied."

Randomized experiment conclusion wording

"The treatment caused a difference in ___ for the experimental units studied."

Random sample conclusion wording

"The results can be generalized to the population sampled."