# CHAPTER 7Comparing Variables of Ordinal or Dichotomous Scales: Spearman Rank-Order, Point-Biserial, and Biserial Correlations

## 7.1 Objectives

In this chapter, you will learn the following items:

- How to compute the Spearman rank-order correlation coefficient.
- How to perform the Spearman rank-order correlation using SPSS
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- How to compute the point-biserial correlation coefficient.
- How to perform the point-biserial correlation using SPSS.
- How to compute the biserial correlation coefficient.

## 7.2 Introduction

The statistical procedures in this chapter are quite different from those in the last several chapters. Unlike this chapter, we had compared samples of data. This chapter, however, examines the relationship between two variables. In other words, this chapter will address how one variable changes with respect to another.

The relationship between two variables can be compared with a correlation analysis. If any of the variables are ordinal or dichotomous, we can use a nonparametric correlation. The Spearman rank-order correlation, also called the Spearman's *ρ*, is used to compare the relationship between ordinal, or rank-ordered, variables. The point-biserial and biserial correlations are used to compare the relationship between two variables if one of the variables is dichotomous. The parametric equivalent to these correlations is the Pearson product-moment correlation.

In this chapter, we will describe how to perform and interpret a Spearman rank-order, point-biserial, and biserial ...