AP STATS U3

Sample Survey

An inquiry that asks questions of individuals drawn from a population (such as a poll)

Census

A sample that consists of the entire population

Population

The entire group about whom a statistician hopes to learn

Sample

A portion of a population examined to learn about that population

Population Parameter

A numerical attribute for an entire population (rarely known)

Sample Statistic

A numerical attribute calculated for sampled data and used to infer the associated population parameter

Sample Size

The number of individuals

Randomization

Each individual is given a fair

Representative

The sample statistics from a sample accurately reflect the population parameters

Simple Random Sampling (SRS)

Each combination of n individuals has an equal chance of selection

Stratified Random Sampling

Population is divided into homogeneous strata and random samples are proportionally drawn from each

Cluster Sampling

Entire heterogeneous groups ("clusters") are randomly selected; each cluster represents the population

Systematic Sampling

Subjects are listed and one subject is selected

Sampling Variability

The natural tendency of randomly drawn samples to differ from one another

Sampling Bias

Systematic failure of a sampling method to properly represent its population

Voluntary Response Bias

Individuals must volunteer or take action to be included in a sample

Convenience Sampling Bias

Subjects are chosen because they are conveniently available

Undercoverage Bias

Some portion of the population is not sampled or has a reduced chance of being included

Nonresponse Bias

A substantial fraction of those sampled fail to respond

Response Bias

Anything in survey design that influences responses (such as leading wording)

Observational Study

A study in which researchers do not assign treatments; they simply observe

Retrospective Study

Subjects are selected and previous conditions/behaviors are observed

Prospective Study

Subjects are selected and followed into the future to observe outcomes

Experiment

Researchers control factor levels

Completely Randomized Design

Every subject has an equal chance of receiving each treatment

Factor

An explanatory variable controlled by the experimenter

Response Variable

The variable whose outcomes are compared across treatments

Level

The specific value chosen for a factor

Treatment

The applied combination of factor levels

Control Group

A baseline or null treatment used for comparison

Subject / Experimental Unit

The individual or object on which an experiment is performed

Randomization (Experiment)

Subjects must be assigned to treatments at random

Replication

Each treatment is applied to multiple subjects

Statistically Significant

An observed difference too large to be explained by natural variation alone

Single-Blind

Either subjects OR evaluators do not know which treatment is assigned

Double-Blind

Both subjects AND evaluators do not know which treatment is assigned

Placebo

A treatment known to have no effect

Placebo Effect

A perceived response to an ineffective treatment

Blocking

Grouping subjects by uncontrollable attributes to reduce variability

Randomized Block Design

Randomization occurs within blocks only

Confounding Variable

When the effects of two variables cannot be separated

Matched Pairs Design

Subjects are paired (or one subject receives both treatments) to reduce variability