We use the following (unbiased) formula to define kurtosis:
kurtosis = { [n(n+1) / (n -1)(n - 2)(n-3)] sum[(x_i - mean)^4] / std^4 } - [3(n-1)^2 / (n-2)(n-3)]
where n is the number of values, mean is the {@link Mean} and std is the{@link StandardDeviation}
Note that this statistic is undefined for n < 4. Double.Nan
is returned when there is not sufficient data to compute the statistic.
Note that this implementation is not synchronized. If multiple threads access an instance of this class concurrently, and at least one of the threads invokes the increment()
or clear()
method, it must be synchronized externally.
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