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A variable is a characteristic or attribute that can assume different values.

Random variable

Data

A population consists of all subjects (human or otherwise) that are being studied.

Census

A sample is a group of subjects selected from a population.

Descriptive statistics consists of the collection, organization, summarization, and presentation of data.

Inferential statistics consists of generalizing from samples to populations, performing estimations and hypothesis tests, determining relationships among variables, and making predictions.

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Qualitative variables are variables that have distinct categories according to some

characteristic or attribute.

Quantitative variables are variables that can be counted or measured.

Discrete variables assume values that can be counted.

Continuous variables can assume an infinite number of values between any two specific values. They are obtained by measuring. They often include fractions and decimals.

The nominal level of measurement classifies data into mutually exclusive (non-overlapping) categories in which no order or ranking can be imposed on the data.

The ordinal level of measurement classifies data into categories that can be ranked; however, precise differences between the ranks do not exist.

The interval level of measurement ranks data, and precise differences between units of measure do exist; however, there is no meaningful zero.

The ratio level of measurement possesses all the characteristics of interval measurement, and there exists a true zero. In addition, true ratios exist when the same variable is measured on two different members of the population.