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Why You Don’t Always Get the Correlation You Expect

Stats With Cats Blog

If you’ve ever taken a statistics class on correlation, you’ve probably come to expect that a large value for a correlation coefficient, either positive or negative, means that there is a noteworthy relationship between two phenomena. This is not always the case. Furthermore, a small correlation may not always mean there is no relationship between the phenomena.

Correlation Size Doesn’t Always Matter

That's not what I expectedThat’s not what I expected.

A small correlation coefficient does not necessarily imply a lack of a relationship any more than a large correlation coefficient implies a strong relationship. It depends on the type of relationship and the data used to characterize it. This is important because analysts often devote all their time investigating large correlations while disregarding relationships that have small correlation coefficients, especially if they don’t have an expectation for what a good value might actually be.

Statistical Reasons for Small Correlations

There are several statistical…

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