AP Stats U1P2 Vocab

Population

The entire group of items/individuals that we want information about.

Parameter

A number that describes some characteristic of a population.

Sample

A subset of the population from which we collect data.

Statistic

A number that describes some characteristic of a sample.

Census

An attempt to contact every item/individual in the entire population.

Observational Unit

An item/individual described in a data set or statistical study.

Variable

A characteristic that can take different values for different observational units.

Experiment

We deliberately impose some treatment on (do something to) individuals in order to observe their responses. This includes randomization of subjects to treatment groups.

Response Variable

Measures an outcome of a statistical study

Explanatory Variable

May help explain/predict changes in a response variable

Levels

The possible values of a factor

Observational Study

We observe individuals and measure variables of interest but do not impose treatments

Retrospective

When the data about the units in an observational study are gathered from the PAST

Prospective

When the data about the units in an observational study are gathered both at a select point in time and into the FUTURE

Survey

An observational study in which data are collected from people by asking them a common set of questions

Extraneous Variables

Variables other than the explanatory variable that may have an effect on the response variable

Confounding

An extraneous variable associated with both the explanatory and response variables

Random Sampling

Using a chance process to determine which members of a population are chosen for the sample

Simple Random Sampling (SRS)

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

Sampling without Replacement

An individual from a population can be selected only ONCE. Do this for an SRS.

Sampling with Replacement

An individual from a population can be selected MORE than once.

Strata

Groups of individuals that share characteristics thought to be associated with the variables being measured in a study

Stratified Random Sample

Selected by choosing an SRS from each stratum and combining the SRSs into one overall sample

Clusters

Groups of individuals that are located near each other

Cluster Random Sample

Selected by choosing an SRS of clusters and including each member of the selected clusters in the sample

Systematic Random Sample

Selected from an ordered arrangement of the population by randomly selecting one of the first k individuals in the population and choosing every kth individual thereafter

Convenience Sample

Consists of members of the population that are EASY to reach

Bias

A design shows this if the resulting sample statistic is likely to under/overestimate the population parameter due to a flaw in the data collection process

Voluntary Response Sample

Consists of people who CHOOSE to be in the sample by responding to a general invitation

Undercoverage

When some members of the population are less likely to be chosen or cannot be chosen for a sample

Nonresponse

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

Response Bias

When responses to a survey question consistently differ from the truth in the same way

Control Group

Used to provide a baseline for comparing the effects of other treatments. May be given an inactive treatment, active treatment, or no treatment at all

Placebo

A treatment that has no active ingredient but is otherwise like the other treatments

Placebo Effect

Some subjects in an experiment will respond favorably to any treatment, even an inactive treatment

Double-Blind

An experiment where neither the subjects nor those interacting with them and measuring the response variable know which treatment a subject is receiving

Single-Blind

An experiment where either the subjects or the people interacting with them and measuring the response variable don't know which treatment a subject is receiving

Random Assignment

The treatments are assigned to experimental units (or experimental units are assigned to treatments) using a chance process

Completely Randomized Design

The experimental units are assigned to the treatments completely at random

Replication

Multiple experimental units are assigned to each treatment

Meaning: "use enough experimental units"

Direct Control

Keeping the values of some extraneous variables the same for all experimental units

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

Blocking Variable

The variable that is used to form the blocks

Randomized Block Design

The random assignment of experimental units to treatments is carried out separately within each block so all treatment occur within each block

Matched Pairs Design

Uses blocks of size 2 to compare two treatments

Statistically Significant

When an observed difference in responses between the groups is so large that it is unlikely to be explained by chance variation in the random assignment

Randomized Distribution

The distribution of a statistic generated by repeatedly reassigning the response values to treatment groups