IBM SPSS Tutorial – Part 08 – Correlations

The following is a good guide for choosing a statistical test:

The Pearson product-moment correlation coefficient (Pearson’s correlation, for short) is a measure of the strength and direction of association that exists between two variables. The measurement level of your two variables should be Scale. Examples of variables that meet this criterion include revision time (measured in hours), intelligence (measured using IQ score), exam performance (measured from 0 to 100), weight (measured in kg), and so forth.

There should be a linear relationship between your two variables. Create a scatterplot using SPSS Statistics, where you can plot the one variable against the other variable, and then visually inspect the scatterplot to check for linearity.

A Pearson’s correlation attempts to draw a line of best fit through the data of two variables, and the Pearson correlation coefficient, r, indicates how far away all these data points are from this line of best fit (i.e., how well the data points fit this model/line of best fit). 

See this example:

and this example:

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