Computes the significance of x' in a Gaussian distribution with mean= mean'
(default 0.0) and standard deviation= sd' (default 1.0); that is, it returns<br> the area which farther from the mean than x' is.
The null hypothesis is roughly that x' is zero; you must specify your<br> alternative hypothesis (H1) via the tails' parameter, which must be :both,
:positive or :negative. The first corresponds to a two-tailed test: H1 is that x' is not zero, but you are not specifying a direction. If the parameter is<br> :positive, H1 is that x' is positive, and similarly for :negative.