Statistics is the science of collecting, analyzing, presenting, and interpreting data as well as of making decisions based on such analyses

Descriptive statistics consists of methods for organizing, displaying, and describing data by using tables, graphs, and summary measures

Inferential statistics consists of methods that use sample results to help make decisions or predictions about a population

A population consists of all elements whose characteristics are being studied
The population that is being studied is also called the target population

A portion of the population selected for study is referred to as a sample

A survey that includes every member of the population is called a census
The technique of collecting information from a portion of the population is called a sample survey

A sample that represents the characteristics of the population as closely as possible is called a representative sample

A sample drawn such that each element of the population has a chance of being selected is called a random sample
If all samples of the same size have the same chance of being selected, it is called simple random sampling

An element or member of a sample or population is a specific subject or object about which information is collected

The value of a variable for an element is called an observation or measurement

A variable is a characteristic under study that assumes different values for different elements
In contrast to a variable, the value of a constant is fixed

A data set is a collection of observations on one or more variables

A variable that can be measured numerically is called a quantitative variable
The data collected on a quantitative variable are called quantitative data

A variable that cannot assume a numerical value but can be classified into categories is called a qualitative or categorical variable
The data collected on such a variable are called qualitative data

Data collected on different elements at the same point in time or for the same period of time are called cross section data

Data collected on the same element for the same variable at different points in time or for different periods of time are called time series data