def backtested_periods(backtest_statistics):
    """
    Helper function for organizing column labels and their corresponding index in backtest_statistics.

    :param backtest_statistics: (pd.DataFrame) Ex-post performance of efficient frontier portfolios.
    :return: (dict) Dictionary of column labels as keys and their corresponding index in backtest_statistics.
    """
    periods = list(backtest_statistics.keys())
    columns = ['1WK', '1MO', '3MO', '6MO', '1YR', '3YR', '5YR', '10YR']
    dictionary = dict(zip(columns, periods))
    return dictionary