import math


def kappa_SE_calc(PA, PE, POP):
    """
    Calculate kappa standard error.

    :param PA: observed agreement among raters (overall accuracy)
    :type PA: float
    :param PE: hypothetical probability of chance agreement (random accuracy)
    :type PE: float
    :param POP: population or total number of samples
    :type POP:int
    :return: kappa standard error as float
    """
    try:
        result = math.sqrt((PA * (1 - PA)) / (POP * ((1 - PE)**2)))
        return result
    except Exception:
        return "None"