def IBA_calc(TPR, TNR, alpha=1):
    """
    Calculate IBA (Index of balanced accuracy).

    :param TNR: specificity or true negative rate
    :type TNR : float
    :param TPR: sensitivity, recall, hit rate, or true positive rate
    :type TPR : float
    :param alpha : alpha coefficient
    :type alpha : float
    :return: IBA as float
    """
    try:
        IBA = (1 + alpha * (TPR - TNR)) * TPR * TNR
        return IBA
    except TypeError:
        return 'None'
