def fscr_score(ftr_t_1, ftr_t, n):
    """Feature Selection Change Rate

    The percentage of selected features that changed with respect to the previous time window

    :param ftr_t_1: selected features in t-1
    :param ftr_t: selected features in t (current time window)
    :param n: number of selected features
    :return: fscr
    :rtype: float
    """
    c = len(set(ftr_t_1).difference(set(ftr_t)))
    fscr = c/n

    return fscr