# The Difference Between Pearson Correlation and Spearman Rank Correlation in Research

For those currently conducting data analysis, correlation tests are commonly used to measure the relationship between two variables. However, not all correlation tests are suitable for every type of data. As we all know, data types and characteristics can vary.

The scale of data measurement plays an important role in determining the appropriate data analysis method. Data measurement scales can be divided into four types: nominal, ordinal, interval, and ratio scales.

The choice of a correlation test that aligns with the data measurement scale is crucial for obtaining accurate and unbiased analysis results. Data measurement scales, such as ordinal or interval, are vital in selecting the proper correlation test. Therefore, choosing the right correlation test based on the data scale is essential for ensuring accurate and unbiased results.

In light of this, Kanda Data has written an article discussing the differences between Pearson correlation and Spearman rank correlation tests.

##### Understanding the Differences Between Pearson Correlation and Spearman Rank Correlation

The Pearson correlation test is the most commonly used method for measuring the relationship between two quantitative variables measured on an interval or ratio scale. This test produces a Pearson correlation coefficient (r), which indicates the strength and direction of the linear relationship between two variables.

The value of r ranges from -1 to 1, where -1 indicates a perfect negative relationship, 0 indicates no relationship, and 1 indicates a perfect positive relationship. A correlation value close to 1 suggests a stronger relationship between the variables.

Next, let’s understand another frequently used correlation test, the Spearman rank correlation test. Spearman rank correlation is a non-parametric method used to measure the relationship between two variables measured on an ordinal scale.

Additionally, Spearman rank correlation can be used when the data does not meet the normality assumption required by the Pearson test. This test calculates the Spearman correlation coefficient (ρ or rs) based on the rank of the data. The value of rs also ranges from -1 to 1, with the same interpretation as the Pearson coefficient described earlier.

##### Assumptions for Using Pearson Correlation and Spearman Rank Correlation

To obtain valid analysis results and unbiased estimates, researchers need to thoroughly understand the assumptions required for these tests. When choosing to use the Pearson correlation test, the assumptions are that the data is on an interval or ratio scale, normally distributed, and free of extreme outliers. Extreme outliers can affect the analysis results.

For the Spearman rank correlation test, the data can be ordinal. Moreover, this test does not require normal distribution, making it suitable for data that does not meet the normality assumption. Interval or ratio scale data that are not normally distributed can also use the Spearman rank correlation test.

##### Case Study Examples to Understand the Differences Between These Two Tests

To provide better understanding, let’s look at an example of a case study on the relationship between study hours and student exam scores. A researcher wants to study the relationship between the number of study hours and student exam scores.

Both variables are measured on an interval scale (number of study hours and exam scores). Since the data meets the normality assumption and the relationship between the variables is assumed to be linear, the Pearson correlation test is the appropriate choice. For example, if the result shows r = 0.8, this indicates a strong positive relationship between the number of study hours and exam scores.

An example of a case study using the Spearman rank correlation test can be seen in research on the relationship between employee motivation and performance. Since motivation and performance data are measured on an ordinal scale and may not meet the normality assumption, the Spearman rank correlation test is more suitable.

For instance, a result of rs = 0.73 indicates that the higher an employee’s motivation to perform at work, the better their performance. This suggests a fairly strong positive relationship.

##### Conclusion

The Pearson correlation test and Spearman rank correlation test are two different methods for measuring the relationship between two variables, and they have different applications depending on the type of data and required assumptions.

The Pearson correlation test is suitable for interval or ratio data that meets the normality assumption, while the Spearman rank correlation test is more flexible and can be used for ordinal data or data that does not meet the normality assumption.

Understanding these differences is important for researchers to choose the most appropriate correlation test, ensuring more accurate analysis results and valid interpretations. This concludes the article from Kanda Data for this occasion. We hope it is beneficial and adds educational value to those in need. Stay tuned for updates from Kanda Data next week. Thank you.