4.1 and 4.2 vocabulary

Population

The entire group of individuals about which we want information.

Census

Collects data from every individual in the population.

Sample

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

Sample Survey

A study that collects data from a sample to learn about the population.

Convenience Sampling

Selects individuals from the population who are easy to reach.

Bias

Occurs if a study is likely to underestimate or overestimate the value.

Voluntary Response Sampling

Allows people to choose to be in the sample by responding to a general invitation.

Random Sampling

Involves using a chance process to determine which members of a population are included in the sample.

Simple Random Sample (SRS)

Chosen so that every group of n individuals has an equal chance to be selected.

Sampling Without Replacement

An individual can be selected only once.

Sampling With Replacement

An individual can be selected more than once.

Table of Random Digits

A long string of digits where each entry is equally likely to be any digit from 0-9.

Strata

Groups of individuals in a population sharing characteristics thought to be associated with variables being measured.

Stratified Random Sampling

Selects a sample by choosing an SRS from each stratum.

Cluster

A group of individuals in the population located near each other.

Cluster Sampling

Selects a sample by randomly choosing clusters and including all members of the selected clusters.

Systematic Random Sampling

Selects from an ordered population by choosing one of the first k individuals and every k-th thereafter.

Multistage Sampling

Combines two or more sampling methods.

Sampling Errors

Errors that come from the act of choosing a sample.

Undercoverage

Occurs when some members of the population are less likely to be chosen.

Sampling Frame

The list from which the sample is chosen.

Nonresponse

Occurs when an individual chosen cannot be contacted or refuses to participate.

Response Bias

A systematic pattern of inaccurate answers to a survey question.

Observational Study

Observes individuals and measures variables of interest without influencing responses.

Response Variable

Measures an outcome of a study.

Explanatory Variable

May help explain or predict changes in a response variable.

Confounding

Occurs when two variables are associated in a way that their effects cannot be distinguished.

Experiment

Deliberately imposes treatments on individuals to measure their responses.

Placebo

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

Treatment

A specific condition applied to individuals in an experiment.

Experimental Unit

The object to which a treatment is randomly assigned.

Factor

An explanatory variable that is manipulated in an experiment.

Levels

The different values of a factor in an experiment.

Control Group

Used to provide a baseline for comparing the effects of other treatments.

Placebo Effect

Some subjects respond favorably to any treatment, even an inactive treatment.

Double-Blind Experiment

Neither the subjects nor those measuring responses know which treatment is given.

Single-Blind Experiment

Either the subjects or the people measuring responses do not know which treatment is given.

Random Assignment

Experimental units are assigned to treatments using a chance process.

Control (experimental design)

Keeping other variables constant for all experimental units.

Replication

Giving each treatment to enough experimental units to distinguish effects from chance variation.

Comparison

Use a design that compares two or more treatments.

Randomized Block Design

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

Matched Pairs Design

Common experimental design that uses blocks of size 2 for comparing two treatments.