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Statistical techniques

Correlation

4.1 The correlation coefficient (r)

Regression analysis attempts to find the straight line relationship between two
variables. Correlation is concerned with establishing how strong the straight line
relationship is. Correlation can be positive or negative:

Positive correlation means that high values of one variable are associated with high
values of the other and that low values of one are associated with low values of the
other.

y y

x x
Strong positive Perfect positive

Negative correlation means that low values of one variable are associated with high
values of the other and vice versa.

y y

x x
Strong negative Perfect negative

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