mad(x, center, constant=1.4826, na.rm = false)
mad provides a scale estimate based on the
median absolute deviation.
The actual value calculated is
constant * (median(abs(x - center)))
with the default value of
center being median(x).
If na.rm is true then NA
values are stripped from x before computation takes place.
If this is not done then an NA value in
x will cause mad to return NA.