AP Statistics Chapter 4

Sample

A part of the population that we actually examine in order to gather information.

Population

The entire group of individuals that we want information about.

Census

An attempt to contact every individual in the entire population.

Observational study

Observes individuals and measures variables of interest but does not attempt to influence the responses.

Experiment

Deliberately imposes some kind of treatment on individuals in order to observe their responses.

Sampling Method

The process used to choose the sample from the population.

Voluntary Response Sampling

A sample consisting of people who choose themselves by responding to a general appeal; over represents those with strong

Convenience Sampling

A sampling method which chooses individuals that are easy to reach.

Bias

The design of a study is biased if it systematically favors certain outcomes.

SRS (Simple Random Sample)

A sample of size $n$ where every set of $n$ individuals has an equal chance to be the sample actually selected.

Systematic Random Sampling

Randomly picking the first item or subject

Probability Sample

Any method of sampling that utilizes some form of random selection.

Stratified Random Sample

First divide the population into similar groups (strata)

Cluster Sampling

Total population is divided into groups (clusters)

Multistage Sampling Design

Involves constructing clusters (stage 1) and then randomly selecting elements from within each selected cluster (stage 2 or more).

Response Bias

Can be caused by the behavior of the respondent or of the interviewer.

Undercoverage

Occurs when some groups in the population are left out of the process of choosing the sample.

Nonresponse

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

Wording of Questions

The way questions are phrased

Sampling Frame

The actual set of units from which a sample has been drawn.

Causation

Indicates a relationship between two events where one event is affected by the other.

Lurking Variable

An unseen variable that creates an apparent association between two other variables (common response).

Confounding

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

Experimental Units

The individuals on which the experiment is done.

Subjects

The term for experimental units when they are human beings.

Treatments

A specific experimental condition applied to the units.

Factors

The explanatory variables in an experiment.

Level

The value of each factor when studying the effects of several factors.

Control Group

A group that receives a placebo or no treatment

Placebo Effect

An effect that occurs when a dummy treatment (placebo) results in an expectation of a cure.

Principle of Experimental Design: Comparison

Use a design that compares two or more treatments.

Principle of Experimental Design: Randomization

The use of impersonal chance to assign subjects to treatments.

Principle of Experimental Design: Control

Controlling the effects of lurking variables on the response

Principle of Experimental Design: Replication

Repeating the experiment on many subjects to reduce chance variation in the results.

Statistically Significant

An observed effect too large to attribute plausibly to chance.

Completely Randomized Design

All the experimental units are allocated at random among all the treatments.

Double-blind

An experiment where neither the subject nor those interacting with them and measuring their responses know which treatment is being received.

Single-blind

An experiment where one party (the subject or the person measuring responses) knows the treatment but the other does not.

Block

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

Randomized Block Design

The random assignment of experimental units to treatments is carried out separately within each block.

Matched Pairs Design

A common form of blocking for comparing just two treatments