Statistics is the science of collecting, viewing, and analyzing data. Typically, the data (the noun "data" is plural) arise as observed characteristics on a selected group of individuals. These individuals, which may be any entities with common features, often represent a larger group of individuals called the population.

This definition of statistics stands in contrast to the everyday perception of statistics as numerical summaries and colorful graphs. We are constantly bombarded by government, business, and sports statistics and their accompanying graphs. Summaries such as these are part of the science of statistics, but they are not its essential core. The core consists of making meaningful statements about the population of individuals based on the information contained in the measured group of individuals.

Data is collected on a group of individuals (hopefully) obtained by modern sampling methods (make preceding a hyperlink). The data consist of measured or observed values on certain common characteristics or attributes of the individuals. The only characteristics of interest vary from individual to individual in the population; consequently, they are called variables.

The goal of data analysis is to make statements about properties of variables, individually or collectively. Variables are classified according to their use in statistics. The major division classifies variables according to whether they are numerical or categorical.

Numerical variables are further divided into whether they are discrete (i.e., the possible values are finite or countable) or continuous (i.e., the possible values form a range or interval). Most commonly, a discrete numeric variable has values which are counts, i.e., 0, 1, 2, etc.

Categorical variables take on values from a finite set of possible levels. A level is a label for a non-numeric value. If the possible levels are ordered, the categorical variable is said to be ordered or ranked.

Exercise 1 gives a series of statistical situations in which the objective is to identify the individual, specify the variable type, and give possible values of the variable.