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LaTeX Math Block
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\rho_P(x,y) = \frac{{\rm cov}(x,y)}{\sigma(x) \sigma(y)}

where

LaTeX Math Inline
bodyx=\{ x_1, \, x_2, \, ... x_n \}
and
LaTeX Math Inline
bodyy=\{ y_1, \, y_2, \, ... y_n \}

finite arrays of

LaTeX Math Inline
bodyx
-variable and
LaTeX Math Inline
bodyy
-variable values

LaTeX Math Inline
body{\rm cov}(x,y)

covariance between

LaTeX Math Inline
bodyx
-variable and
LaTeX Math Inline
bodyy
-variable

LaTeX Math Inline
body\sigma(x)
,
LaTeX Math Inline
body\sigma(y)

standard deviation of

LaTeX Math Inline
bodyx
-variable and
LaTeX Math Inline
bodyy
-variable


Pearson correlation coefficient ranges between -1 and 1 and indicates how accurately the two variables can be approximated by a linear correlation:

...

  • Maximum value 
    LaTeX Math Inline
    body\rho_p(x,y) = + 1
    relates to perfect linear correlation with 
    LaTeX Math Inline
    bodya>0
     (see also Fig. 1)

  • Zero value 
    LaTeX Math Inline
    body\rho_p(x,y) = 0
    relates to absence of correlation between 
    LaTeX Math Inline
    bodyx
     and 
    LaTeX Math Inline
    bodyy
      (see also Fig. 2)

  • Minimum value 
    LaTeX Math Inline
    body\rho_p(x,y) = - 1
     relates to perfect linear correlation with 
    LaTeX Math Inline
    bodya<0
     (also called anti-correlation) (see also Fig. 3)


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Fig. 1. Highly correlated variablesFig. 2. Poorly correlated variablesFig. 3. Highly anti-correlated variables


See also

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Formal science / Mathematics / Statistics Statistical correlation 

Statistical correlation metrics @ review ]