# The Practice of Statistics 4e - Ch 4 Vocab

Anonymity

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

Bias

The design of a statistical study systematically favors certain outcomes.

Block

A group of experimental units known before the experiment to be similar in some way that is expected to affect response.

Census

A study that attempts to collect data from every individual in the population.

Cluster sample

All individuals in the chosen group are included in the sample.

Completely randomized design

When the treatments are assigned to all the experimental units completely by chance.

Confidentiality

A basic principle of data ethics that requires individual data to be kept private.

Confounding

When two variables are associated in such a way that their effects on a response variable cannot be distinguished from each other.

Control

Done by using a comparative design and ensuring the only systematic difference between the groups is the treatment.

Control group

An experimental group whose primary purpose is to provide a baseline for comparing the effects of the other treatments.

Convenience sample

A sample selected by taking the members of the population that are easiest to reach

Double-blind

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

Experiment

Deliberately imposes some treatment on individuals to measure their responses.

Experimental units

Individuals to which treatments are applied.

Explanatory variable

A variable that helps explain or influences changes in the other variable.

Factor

Another name for the explanatory variable in an experiment

Inference

Using information from a sample to draw conclusions about the larger population.

Using the results of an experiment to conclude that the treatments caused the difference in responses.

Informed consent

Individuals must be made aware in advance about the nature of a study and any risk of harm, then agree in writing.

Institutional review board

All planned studies must be approved in advance and monitored to protect the safety and well-being of the participants.

Lack of realism

When the treatments, the subjects, or the environment of an experiment are not realistic.

Level

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

Lurking variable

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

Margin of error

A numerical estimate of how far the sample result is likely to be from the truth about the population due to sampling variability.

Matched pair

A common form of blocking for comparing just two treatments.

Nonresponse

Occurs when a selected individual cannot be contacted or refuses to cooperate

Nonsampling error

Some common examples are nonresponse, response bias, and errors due to question wording.

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.

Population

In a statistical study, the entire group of individuals about which we want information.

Random assignment

Use some chance process to assign experimental units to treatments.

Random sampling

The use of chance to select a sample

Randomized block design

Random assignment of treatments is carried out separately within each block.

Replication

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 bias

A systemic pattern of incorrect responses.

Response variable

A variable that measures an outcome of a study.

Sample

The part of the population from which we actually collect information.

Sampling error

Mistakes made in the process of taking a sample. Bad sampling methods and undercoverage are common types.

Sampling frame

The list from which a sample is actually chosen.

Simple random sample (SRS)

Gives every possible sample of a given size the same chance to be chosen.

Single-blind

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

Statistically significant

An observed effect so large that it would rarely occur by chance.

Strata

Groups of individuals in a population that are similar in some way that might affect their responses.

Stratified random sample

First classify the population into groups of similar individuals then choose a separate SRS from each group to form the full sample.

Subjects

Experimental units that are human beings.

Table of random digits

A long string of the digits 0, 1, 2, 3, 4, 5, 6, 7, 8, 9

Treatment

A specific condition applied to the individuals in an experiment.

Undercoverage

Occurs when some members of the population are left out of the sampling frame

Wording of questions

The most important influence on the answers given to a survey.