def calc_acceleration_abc(empirical_influence):
    """
    Calculates the acceleration constant for the approximate bootstrap
    confidence (ABC) intervals.

    Parameters
    ----------
    empirical_influence : 2D ndarray.
        Should have one row for each observation. Should have one column for
        each parameter in the parameter vector being estimated. Elements should
        denote the empirical influence of the associated observation on the
        associated parameter.

    Returns
    -------
    acceleration : 1D ndarray.
        Contains the ABC confidence intervals' estimated acceleration vector.

    References
    ----------
    Efron, Bradley, and Robert J. Tibshirani. An Introduction to the Bootstrap.
        CRC press, 1994. Section 22.6, Equation 22.34.
    """
    influence_cubed = empirical_influence**3
    influence_squared = empirical_influence**2
    numerator = influence_cubed.sum(axis=0)
    denominator = 6 * (influence_squared.sum(axis=0))**1.5
    acceleration = numerator / denominator
    return acceleration