Pearson’s product moment correlation coefficient
Pearson’s product moment correlation coefficient is denoted
as ρ for a population parameter and as r for a sample
statistic. It is used when both variables being studied are
normally distributed. This coefficient is affected by extreme
values, which may exaggerate or dampen the strength of
relationship, and is therefore inappropriate when either or
both variables are not normally distributed. For a correlation
between variables x and y, the formula for calculating the
sample Pearson’s correlation coefficient is given by