AP Statistics Chapter 4 Vocab

Census

Attempt to contact every individual in the entire population.

Treatment

A specific experimental condition applied to the units/subjects

Bias

Systematically favors certain outcomes

Voluntary Response

Consists of people who choose themselves by responding. Tend to be biased because only those with strong opinions respond.

Factors

The experimental variables in an experiment

Confounding

Two variables are confounded when their effects on a response variable cannot be distinguished from each other. This happens with experiments

Observational Study

Individuals are observed but researchers do not attempt to influence participants' responses

Experiment

Some treatment is imposed on (that is, do something to) individuals in order to observe their responses

Population

The entire group of individuals that we want information about

Sample

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

Experimental Units

The individuals on which the experiment is done. When humans are involved they are referred to as "participants" or "subjects"

Placebo Effect

A response, usually favorable, to a "dummy" treatment

Placebo

A "dummy" treatment

Double-Blind Experiment

Neither the participants nor those who measure the response variable(s) know which treatment a subject receives

Undercoverage

Some members of the population cannot be chosen in a sample

Response Bias

A systematic pattern of inaccurate answers in a survey

Simple Random Sample (SRS)

A sample of size n is chosen in such a way that every group of n individuals in the population has an equal chance to be selected as the sample

Stratified Random Sample

Start by classifying the population into heterogeneous groups, called strata. Then choose a separate SRS in each stratum and combine these SRSs to form the sample

Cluster Sample

Start by classifying the population into homogeneous groups called clusters, then choose an SRS of the clusters. All individuals in the chosen clusters are the sample

Participants/Subjects

The term for the experimental units that are the sample of individuals to which treatments are applied

Convenience Sample

Choosing individuals who are easiest to reach

Non-Response

An individual chosen for the sample cannot be contacted or refuses to participate

Statistically Significant

An observed effect so large that it would rarely occur by chance (threshold 5%).

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.

Matched Pairs

A randomized blocked experiment in which each block consists of a matching pair of similar experimental units. Chance is used to determine which pair gets each treatment. In some cases, a matched pairs design can also be an experiment where a single unit receives both treatments, the order of which is assigned randomly.

systematic sampling

a system for selecting a setup(select every 10th person)

sample survey

a study that collects data from a sample that is chosen to represent a specific population

control

environment the same for all experiental units

replication

more than 1 exp unit/subject in each treatment group

randomization

experimental units or subjects randomly assigned to treatment groups

• used to help account for confounding variables; effects of variables offset each other

comparison

compare treatment groups after- a design that compares 2+ treatments

control group

used to provide a baseline for comparison of the effects of other treatments

confounding variables

“things” going on in background that may impact outcomes; so need random assignment

level

the different values of a factor

single-blind experiment

when either the subjects don’t know which treatment they will have or the people who interactcompletely randomized design with them and measure their response don’t know which subjects are receiving which treatment

completely randomized design

the experimental units are assigned to the treatments completely by chance

• groups don’t have to be same size

blockrandomized blockdesign

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

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

• accounts for variation

• subjects split into blocks

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

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

matched pairs design

a common experimental design for comparing two treatments that uses blocks of size 2

• 2 very similar experimental units are paired and the 2 treatments are randomly assigned within each pair

• each experimental unit receives both treatments in a random order

sampling variability

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

sampling variability and sample size

larger random samples tend to produce estimates that are closer to the true population value than smaller random samples. estimates from larger samples are more precise

statistically significant

when the observed results of a study are too unusual to be explained by chance alone; unlikely to have happened by chance