import math


def pearson_C_calc(chi_square, POP):
    """
    Calculate Pearson's C (C).

    :param chi_square: chi squared
    :type chi_square: float
    :param POP: population or total number of samples
    :type POP: int
    :return: C as float
    """
    try:
        C = math.sqrt(chi_square / (POP + chi_square))
        return C
    except Exception:
        return "None"