\begin{definition}[Definition:Pearson Correlation Coefficient]
Let $X$ and $Y$ be random variables. 
Let the variances of $X$ and $Y$ exist and be finite.
Then the '''Pearson correlation coefficient''' of $X$ and $Y$, typically denoted $\map \rho {X, Y}$, is defined by: 
:$\map \rho {X, Y} = \dfrac {\cov {X, Y} } {\sqrt {\var X \, \var Y} }$
where $\cov {X, Y}$ is the covariance of $X$ and $Y$. 
{{NamedforDef|Karl Pearson|cat = Pearson}}
\end{definition}