def _counter_inc(stats, stat, key, increment=1):
    """
    Helper for incrementing given statistical parameter within given statistical
    bundle.

    :param dict stats: Structure containing all statistics.
    :param str stat: Name of the statistical category.
    :param str key: Name of the statistical key.
    :param int increment: Counter increment.
    :return: Updated structure containing statistics.
    :rtype: dict
    """
    if not stat in stats:
        stats[stat] = {}
    stats[stat][str(key)] = stats[stat].get(str(key), 0) + increment
    return stats
