Data

Information coming from observations, counts, measurements, or responses.

Statistics

The science of collecting, organizing, analyzing, and interpreting data in order to make decisions.

Population

The collection of all outcomes, responses, measurements, or counts that are of interest.

Sample

A subset of a population.

Paramater

A numerical measurement describing a population characteristic.

Statistic

A numerical measurement describing some characteristic of a sample.

Descriptive Statistics

The branch of statistics that involves the orginization, summarization, and display of data.

Inferrential Statistics

The branch of statistics that involves using a sample to draw conclusions about a population.

Qualitative Data

Data that consists of attributes, labels, or nonnumerical entries.

Quantitative Data

Data that consists of numerical measurements or counts.

Nominal Level of Measurement

Qualitative only. Data at this level are categorized using names, labels, or qualities. No mathematical computations can be made at this level.

Ordinal Level of Measurement

Data at this level are qualitative or quantitative. Data at this level can be arranged in order, or ranked, but differences between data entries are not meaningful.

Interval Level of Measurement

Data at this level can be ordered, and you can calculate meaningful differences between data entries. At this level, a zero entry simply represents a position on a scale; the entry is not an inherent zero.

Ratio Level of Measurement

Data at this measurement are similar to data at the interval level, with the added property that a zero entry is an inherent zero. A ratio of two data values can be formed so that one data value can be meaningfully expressed as a multiple of another.

Observational Study

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

Experiment

The act of conducting a controlled test or investigation.

Treatment

A specific experimental condition applied to the units.

Control Group

The group that does not receive the experimental treatment.

Experimental Units

Individuals on whom an experiment is performed.

Placebo

Something presented as a drug, but having no actual effect.

Simulation

The act of imitating the behavior of some situation or some process by means of something suitably analogous (especially for the purpose of study or personnel training)

Survey

Research method in which information is obtained by asking many individuals a fixed set of questions.

Biased

A preference that prevents one from being impartial; prejudice.

Confounding Variable

In an experiment, a variable, other than the independent variable, that could influence the dependent variable.

Placebo Effect

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

Double-Blind Experiment

An experiment in which neither the experimenter nor the participants know which participants received which treatment.

Randomization

A process of choosing the members of the experimental and control groups without bias.

Completly Randomized Design

All experimental units have an equal chance of receiving any treatment.

Blocks

When groups of experimental units with similar charastics are gathered.

Randomized Block Design

Divide subjects with similar characteristics into blocks, and then within each block, randomly assign subjects to treatment groups.

Matched-Pairs Design

Match pairs of people with traits significant to experiment then randomly put one in treatment and one in control.

Replication

The repetition of an experiment in order to test the validity of its conclusion.

Census

A count or measure of the entire population.

Sampling

A count or measure of part of a population.

Sampling Error

The difference between a sample's results and the true result if the entire population had been interviewed.

Random Sample

A sample in which every element in the population has an equal chance of being selected.

Simple Random Sample

A sample of size n selected from the population in such a way that each possible sample of size n has an equal chance of being selected.

Stratified Sample

A sampling design in which the population is divided into several subpopulations, or strata, and random samples are then drawn from each stratum.

Cluster Sample

A sample obtained by selecting a preexisting or natural group, called a cluster, and using the members in the cluster for the sample.

Systematic Sample

A sample in which elements are selected at predetermined intervals.

Convience Sample

A sample chosen without any random mechanism; samples chosen based on ease of selection.