AP Stats Unit 1

Variable

A characteristic whose value may change from one observation to another.

Data

A collection of observations on one or more variables.

Quantitative Data

Data that can be measured and expressed numerically.

Discrete Data

Quantitative data on a variable that correspond to isolated points on a number line.

Continuous Data

Quantitative data on a variable that correspond to an interval of points on a number line.

Categorical Data

Data that can be divided into groups or categories.

Binary Data

Categorical data with two possible outcomes (e.g., 0 or 1, Success or Failure).

Non-Binary Data

Categorical data that can take on more than two categories (e.g., Favorite color, Race, Religion).

Observational Study

A study where the researcher observes and records characteristics of a sample selected from one or more populations.

Experimental Study

A study where the researcher observes how a response variable behaves when one or more explanatory variables are manipulated.

Observational/Experimental Units

The objects from which data is collected.

Causal Relationships

Relationships that can only be determined using a controlled, randomized experimental study.

Correlations

Associative relationships between variables that can be concluded from observational studies.

Selection Bias

When creating a sample, a systematic exclusion of a sector of the population occurs.

Undercoverage Bias

Occurs when some members of a population are totally excluded from the sample frame used for the study.

Voluntary Response Bias

Occurs when people who volunteer to participate in a study are different from those who do not.

Sample

A subset of a population selected for observation and analysis.

Population

The entire group of individuals or instances about whom we hope to learn.

Response Variable

The dependent variable that is being measured in an experiment.

Explanatory Variable

The independent variable that is manipulated in an experiment.

Random Assignment

The process of assigning participants to different groups in a study randomly.

Bias in Sampling

The tendency for samples to differ from the population in a systematic way.

Nonresponse Bias

Data is not obtained from all subjects in a sample, but not because the sampling technique was bad. This occurs when people who are invited to participate in a survey do not respond, either intentionally or unintentionally.

Response Bias

Tools used to gather data result in responses that skew in one direction. In survey sampling, response bias refers to the bias that results from problems in the measurement process.

Measurement Bias

Tools used to gather the data result in systematic and consistent errors.

Experiment

A procedure for investigating the effect of an experimental condition on a response variable.

Experimental units

Individuals on whom an experiment is performed (usually called subjects or participants).

Factor

A variable whose levels are controlled by the experimenter.

Extraneous factor

A variable that is not of interest in the current study but is thought to affect the response variable.

Treatment

The process, intervention, or other controlled circumstance applied to randomly assigned experimental units.

Confounding variable

Associated in a noncausal way with a factor and affects the response.

Direct control

Holding extraneous factors constant so that their effects are not confounded with those of the experimental conditions.

Blocking

When groups of experimental units are similar (have common extraneous factors), it is often a good idea to gather them together into blocks.

Randomized block design

When randomization occurs only within blocks.

Placebo

A treatment known to have no effect, administered so that all groups experience the same conditions.

Placebo effect

The tendency of many human subjects to show a response even when administered a placebo.

Control group

The experimental units assigned to a baseline treatment level, typically either the default treatment, no treatment, or a placebo treatment.

Blind(ing)

Any individual associated with an experiment who is not aware of how subjects have been allocated to treatment groups.

Double-blind

When every individual who can either influence the results or evaluate the results is blinded.