Understanding Statistical Concepts and Variables

Population

A population is the set of all elements that are subjected to a statistical study.

Individual

An individual or statistical unit is each of the elements of the population.

Sample

A sample is a representative subset of the reference population; the number of individuals in a sample is less than that of the population.

Sampling

Sampling is the collection of data to be studied, obtained from a small proportion that is representative of the population.

Value

A value is each of the different results that can be obtained in a statistical study. For example, if you toss a coin 5 times, you get two values: heads and tails.

Data

Data refers to each of the values obtained by performing a statistical study. If you toss a coin 5 times, you get 5 data points: heads, heads, tails, heads, tails.

Statistical Variables

Qualitative Variable

Qualitative variables refer to characteristics or qualities that cannot be measured with numbers. There are two types:

Nominal Qualitative Variable

A nominal qualitative variable presents no numerical methods and does not support a criterion of order.

Ordinal Categorical Variable

An ordinal categorical variable has non-numerical methods in which there is an order.

Quantitative Variable

A quantitative variable is expressed by a number, allowing for arithmetic operations to be performed. There are two types:

Discrete Variable

A discrete variable is one that takes distinct values, meaning it admits no intermediate values between two values.

Continuous Variable

A continuous variable is one that can take values between two numbers.

Frequency Distribution

The frequency distribution or frequency table is a tabular organization of statistical data, assigning each corresponding frequency to the data.

Bar Chart

A bar chart is used to present quantitative data or discrete types. The data are represented by bars of a height proportional to their frequency.

Frequency Polygons

A frequency polygon is formed by linking the ends of the segments represented by the bars. It can also be created by plotting the points representing the frequency and linking them through segments.

Pie Chart

A pie chart can be used for all sorts of variables, but is often used for qualitative variables. The data is represented in a circle so that the angle of each sector is proportional to the corresponding absolute frequency.

Histogram

A histogram is a graphical representation of a variable using bars. They are used for continuous or discrete variables with a large amount of data, which are grouped into classes. In the abscissa axis, basic rectangles are built around the range width and height, representing the absolute frequency of each interval.