AP Stat: Chapter 4 vocab 2

Anonymity

Anonymity

When the names of individuals participating in a study are not known even to the director of the study.

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.

Control

An important experimental design principle. Researchers should control for lurking variables that might affect the response by using a comparative design and ensuring that the only systematic difference between the groups is the treatment administered.

Control group

An experimental group whose primary purpose is to provide a baseline for comparing the effects of the other treatments. Depending on the purpose of the experiment, a control group may be given a placebo or an active treatment.

Double-blind

An experiment in which neither the subjects nor those who interact with them and measure the response variable know which treatment a subject received.

Experiment

Deliberately imposes some treatment on individuals to measure their responses.

Experimental units

The smallest collection of individuals to which treatments are applied.

Explanatory variable

A variable that helps explain or influences changes in a response variable.

Factor

The explanatory variables in an experiment are often called factors.

Inference about cause and effect

Using the results of an experiment to conclude that the treatments caused the difference in responses. Requires a well-designed experiment in which the treatments are randomly assigned to the experimental units.

Level

A specific value of an explanatory variable (factor) in an experiment.

Lurking variable

A variable that is not among the explanatory or response variables in a study but that may influence the response variable.

Observational study

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

Placebo

An inactive (fake) treatment.

Placebo effect

Describes the fact that some subjects respond favorably to any treatment, even an inactive one (placebo).

Random assignment

An important experimental design principle. Use some chance process to assign experimental units to treatments. This helps create roughly equivalent groups of experimental units by balancing the effects of lurking variables that aren’t controlled on the treatment groups.

Randomized block design

Start by forming blocks consisting of individuals that are similar in some way that is important to the response. Random assignment of treatments is then carried out separately within each block.

Replication

An important experimental design principle. Use enough experimental units in each group so that any differences in the effects of the treatments can be distinguished from chance differences between the groups.

Response variable

A variable that measures an outcome of a study.

Single-blind

An experiment in which either the subjects or those who interact with them and measure the response variable, but not both, know which treatment a subject received.

Subjects

Experimental units that are human beings.

Treatment

A specific condition applied to the individuals in an experiment. If an experiment has several explanatory variables, a treatment is a combination of specific values of these variables.