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Pearson's correlation coefficient is the covariance of the two variables divided by the product of their standard deviations. The form of the definition involves a "product moment", that is, the mean (the first moment about the origin) of the product of the mean-adjusted random variables; hence the modifier product-moment in the name.
Pearson was joined by Sir Francis Galton [5] and Walter Frank Raphael Weldon [1] in cautioning scientists to be wary of spurious correlation, especially in biology where it is common [6] to scale or normalize measurements by dividing them by a particular variable or total. The danger he saw was that conclusions would be drawn from correlations ...
The Pearson product-moment correlation coefficient, also known as r, R, or Pearson's r, is a measure of the strength and direction of the linear relationship between two variables that is defined as the covariance of the variables divided by the product of their standard deviations. [4]
The sample Taylor diagram shown in Figure 1 [16] provides a summary of the relative skill with which several global climate models simulate the spatial pattern of annual mean precipitation. Eight models, each represented by a different letter on the diagram, are compared, and the distance between each model and the point labeled “observed ...
The examples are sometimes said to demonstrate that the Pearson correlation assumes that the data follow a normal distribution, but this is only partially correct. [4] The Pearson correlation can be accurately calculated for any distribution that has a finite covariance matrix, which includes
With any number of random variables in excess of 1, the variables can be stacked into a random vector whose i th element is the i th random variable. Then the variances and covariances can be placed in a covariance matrix, in which the (i, j) element is the covariance between the i th random variable and the j th one.
Third, a zero Pearson product-moment correlation coefficient does not necessarily mean independence, because only the two first moments are considered. For example, = (y ≠ 0) will lead to Pearson correlation coefficient of zero, which is arguably misleading. [2]
When only an intercept is included, then r 2 is simply the square of the sample correlation coefficient (i.e., r) between the observed outcomes and the observed predictor values. [4] If additional regressors are included, R 2 is the square of the coefficient of multiple correlation. In both such cases, the coefficient of determination normally ...