def mean(data):
    return sum(data) / len(data)

def median(data):
    s = sorted(data)
    n = len(s)
    mid = n // 2
    return (s[mid] + s[~mid]) / 2

def variance(data):
    m = mean(data)
    return sum((x - m) ** 2 for x in data) / len(data)

def standard_deviation(data):
    return variance(data) ** 0.5