Exercise: Vocabulary, age, and epilepsy, 3

Question 3: What does r = -0.34 mean?

Suggested answer

This is the correlation coefficient. It measures how close to a straight line relationship the data are.

Correlation coefficients, denoted by r for confusing historical reasons, lie between minus one and plus one. A negative correlation coefficient means than large values of one variable are associated with small values of the other variable, a positive correlation coefficient means than large values of one variable are associated with large values of the other variable, Zero correlation coefficient means that there is no linear relationship.

The correlation coefficient r = -0.34 means that there is a weak negative relationship, that is that older people have smalle verbal learning test scores. This is apparent from the scatter diagram.


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