    def get_prob(self):
        if self.total < 5:
            return 0.
        a, b = self.dup + 1, self.nodup + 1
        n = a + b
        p = a / n
        q = b / n
        # Lower edge of the 95% confidence interval, binomial distribution
        return p - 1.96 * math.sqrt(p * q / n)