Possible error when computing standard deviation

[mthh]

The denominator should be n (number of individuals) instead of n - 1 when calculating the variance (and so the standard deviation) for "msd" classification.

In R and in d3-array the variance (and so the standard deviation) is also calculated using n - 1, but I've been told that this formula is used to calculate an unbiased estimator of a sample population while n is used when you have knowledge of the full population (which is our case here, and which is also what is taught in cartography when teaching this kind of classification, at least in France).

Note that:

• mapsf also uses n rather than n - 1,
• Magrit uses n rather than n - 1 since v2.2.3.