a numeric vector containing the values whose kurtosis is to be
computed. NA values are removed in the computation.
Details
If \(N = \mathrm{length}(x)\), then the kurtosis of \(x\)
is defined as: $$N sum_i (x_i-\mathrm{mean}(x))^4 (sum_i
(x_i-\mathrm{mean}(x))^2)^(-2) - $$$$3$$
References
G. Snedecor, W. Cochran. Statistical Methods,
Wiley-Blackwell, 1989