def acc_stats(stats_list):
    """Accumulate a list of sufficient statistics.

    Parameters
    ----------
    stats_list : list
        List of sufficient statistics.

    Returns
    -------
    stats : dict
        Accumulated sufficient statistics.

    """
    new_stats = {}

    for stats in stats_list:
        for key1, model_stats in stats.items():
            if key1 not in new_stats:
                new_stats[key1] = {}
            for key2, value in model_stats.items():
                try:
                    new_stats[key1][key2] += value
                except KeyError:
                    new_stats[key1][key2] = value

    return new_stats