def _estimate_fringe_contrast_statistical(holo):
    """
    Estimates average fringe contrast of a hologram using statistical definition:
    V = STD / MEAN.

    Parameters
    ----------
    holo_data: ndarray
        The data of the hologram.

    Returns
    -------
    Fringe contrast as a float
    """
    axes = holo.axes_manager.signal_axes
    return holo.std(axes) / holo.mean(axes)
