def METHOD_NAME(s, d):
    """Calculates chao1 variance, bias-corrected.
    `s` is the number of singletons and `d` is the number of doubletons.
    From EstimateS manual, equation 6.
    """
    return (s * (s - 1) / (2 * (d + 1)) + (s * (2 * s - 1) ** 2) /
            (4 * (d + 1) ** 2) + (s ** 2 * d * (s - 1) ** 2) /
            (4 * (d + 1) ** 4))