import math


def LR_SE_calc(item1, item2, item3, item4):
    """
    Calculate likelihood ratio +/- standard error.

    :param item1: true positive or false negative (TP or FN)
    :type item1: int
    :param item2: number of actual positives (P)
    :type item2: int
    :param item3: false positive or true negative (FP or TN)
    :type item3: int
    :param item4: number of actual negatives (N)
    :type item4: int
    :return: standard error as float
    """
    try:
        return math.sqrt((1 / item1) - (1 / item2) + (1 / item3) - (1 / item4))
    except Exception:
        return "None"