def METHOD_NAME(self):
    """Return the sample standard deviation for the data (float)."""
    data = list(self.data.values())
    m = self.mean()
    runtotal = 0.0
    for entry in data:
        runtotal += (entry - m) ** 2
    # This is sample standard deviation; population stdev would involve
    # division by len(data), rather than len(data)-1
    return sqrt(runtotal / (len(data) - 1))