def _adjust_prices(hist_data, price_list=None):
    """
    Return modifed DataFrame with adjusted prices based on
    'Adj Close' price. Adds 'Adj_Ratio' column.
    """
    if price_list is None:
        price_list = 'Open', 'High', 'Low', 'Close'
    adj_ratio = hist_data['Adj Close'] / hist_data['Close']
    data = hist_data.copy()
    for item in price_list:
        data[item] = hist_data[item] * adj_ratio
    data['Adj_Ratio'] = adj_ratio
    del data['Adj Close']
    return data
