What Type of Data Is Used for Correlation?


Heather Bennett

What Type of Data Is Used for Correlation?

Correlation is a statistical technique used to determine the relationship between two or more variables. It allows us to understand the strength and direction of the relationship between these variables. However, before we dive into understanding correlation, it’s important to know the different types of data that are used for correlation analysis.

Types of Data

In statistics, data can be classified into four main types:

  • Nominal Data: This type of data consists of categories or labels with no specific order. Examples include gender (male/female), colors (red/blue/green), or car models (sedan/suv/hatchback).
  • Ordinal Data: Ordinal data is similar to nominal data but has an inherent order or ranking.

    For instance, ratings given on a scale from 1 to 5 or educational levels categorized as high school, undergraduate, graduate.

  • Interval Data: Interval data has a numerical value with equal intervals between each value. Temperature measured in Celsius or Fahrenheit is an example of interval data.
  • Ratio Data: Ratio data is similar to interval data but has a clear absolute zero point. Examples include weight, height, time, or income.

Data Requirements for Correlation Analysis

In correlation analysis, we typically use interval or ratio level data. This is because correlation measures the strength and direction of the linear relationship between two continuous variables. Variables such as height and weight can be measured on an interval or ratio scale and can be effectively analyzed using correlation techniques.

Note that nominal and ordinal data are not suitable for correlation analysis because they lack the necessary numerical properties required for calculating correlation coefficients.


To better understand this concept, let’s consider an example:

Suppose we want to investigate the relationship between hours of study and exam scores. Both variables, hours of study and exam scores, can be measured on a continuous scale and are therefore suitable for correlation analysis.

We can collect data from a group of students by recording the number of hours they studied and their corresponding exam scores. By applying correlation analysis to this data, we can determine if there is a positive or negative relationship between study hours and exam scores, as well as the strength of that relationship.


Correlation analysis is a powerful statistical tool used to examine the association between variables. However, it’s essential to use interval or ratio level data for accurate correlation calculations. Nominal and ordinal level data do not possess the necessary properties for correlation analysis.

By understanding the types of data suitable for correlation analysis, you can ensure that you’re using the right data when investigating relationships between variables.

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