Returns the mean, the sample variance (divisor \(n - 1\)), the moment-ratio skewness \(g_1 = m_3 / m_2^{3/2}\) and the moment-ratio kurtosis \(b_2 = m_4 / m_2^2\) (not excess kurtosis, so a Gaussian sample gives values near 3), where \(m_k\) is the \(k\)-th sample central moment with divisor \(n\).