def group_metrics(metric):
    """Return the group of a metric"""
    if metric in ['nme', 'mbe', 'sd_diff', 'corr']:
        return "common"
    elif metric in ['extreme_5', 'extreme_95']:
        return 'extremes'
    elif metric in ['skewness', 'kurtosis', 'overlap']:
        return 'distribution'
    else:
        return None