'Return results as a multiindex dataframe'

@property
def summary_frame(self):

    df = []
    for key in self.results:
        tmp = self.results[key]['stat'].copy()
        tmp.loc[:, 'Effect'] = key
        df.append(tmp.reset_index())
    df = pd.concat(df, axis=0)
    df = df.set_index(['Effect', 'index'])
    df.index.set_names(['Effect', 'Statistic'], inplace=True)
    return df
