Given an OTS of length \(T\) with range \(\mathcal{S}=\{s_0, s_1, s_2, \ldots, s_n\}\) (\(s_0 < s_1 < s_2 < \ldots < s_n\)),
\(\overline{X}_t=\{\overline{X}_1,\ldots, \overline{X}_T\}\), the function computes the
estimated IOV given by \(\widehat{IOV}=\frac{4}{n}\sum_{k=1}^{n-1}\widehat{f}_k(1-\widehat{f}_k)\),
where \(\widehat{f}_k\) is the standard estimate of the cumulative marginal probability
for state \(s_k\) computed from the series \(\overline{X}_t\).