Statistics and Sampling Methods

A comprehensive review of key vocabulary terms related to population sampling and experimental designs.

Population

The entire group you want information about.

Sample

A subset of the population from which data is collected.

Census

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

Sampling Frame

The list of individuals from which a sample is drawn.

Random Sampling

A method that gives every individual an equal chance of being selected.

Simple Random Sample (SRS)

A sampling method where every group of a given size has an equal chance of being chosen.

Stratified Random Sample

A sample where the population is divided into groups (strata), and a random sample is taken from each group.

Cluster Sample

A sampling method where the population is split into clusters, some clusters are randomly selected, and all individuals in those clusters are surveyed.

Systematic Sample

A sample where every nth individual is selected from a list after a random starting point.

Convenience Sample

A sample drawn from individuals who are easiest to reach, often leading to bias.

Voluntary Response Sample

A sample where individuals choose to respond, usually resulting in bias.

Bias

A consistent error that results in an over- or underestimation of the true population value.

Undercoverage

A sampling error where some members of the population are not represented in the sample.

Nonresponse Bias

Bias introduced when selected individuals do not respond to the survey.

Response Bias

Bias caused by inaccurate responses, often due to wording, pressure, or dishonesty.

Wording of Questions

The phrasing of survey questions, which can influence respondents’ answers and introduce bias.

Observational Study

A study that observes individuals without attempting to influence them.

Experiment

A study that applies treatments to individuals to measure their responses.

Explanatory Variable

A variable that may explain or influence changes in another variable (independent variable).

Response Variable

The outcome or result measured in a study (dependent variable).

Confounding

When the effects of two variables on the response variable cannot be separated.

Treatment

A specific condition applied to the experimental units.

Experimental Units

The individuals on whom an experiment is performed; called subjects when they are people.

Factors

The explanatory variables in an experiment.

Levels

The specific values of a factor used in the treatments.

Control

A principle of experimental design used to limit confounding by keeping other variables constant.

Random Assignment

Using chance to assign experimental units to different treatment groups.

Replication

Using enough subjects to distinguish a real treatment effect from chance variation.

Control Group

A group that receives no treatment or a standard treatment for comparison purposes.

Completely Randomized Design

An experimental design where all experimental units are randomly assigned to treatments.

Randomized Block Design

An experimental design that groups similar units into blocks and randomly assigns treatments within each block.

Matched Pairs Design

A type of block design where subjects are paired based on similarity or receive both treatments in random order.