def incoordination_score(self, data_frame):
        """
            This method calculates the variance of the time interval in msec between taps

            :param data_frame: the data frame
            :type data_frame: pandas.DataFrame
            :return is: incoordination score
            :rtype is: float

        """
        diff = data_frame.td[1:-1].values - data_frame.td[0:-2].values
        inc_s = np.var(diff[np.arange(1, len(diff), 2)], dtype=np.float64) * 1000.0
        duration = math.ceil(data_frame.td[-1])
        return inc_s, duration