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# INTRODUCTION

Correlation coefficients give a numerical value to the strength and direction of a relation between variables. This chapter covers correlation techniques used with interval, ratio scale and ordinal scale variables. The chi square test of independence covered in Chapter 15 can test the association between two nominal variables. The current chapter covers Pearson’s r, Spearman’s ρ and Kendall’s τ. The correlation statistics that measure the strength and direction of a relationship are called correlation coefficients and their values range from −1.0 to +1.0. The sign of the correlation coefficient (+ or −) tells us whether any relation is positive or negative. Figure 8.1 uses scatter plots to show some examples ...

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