docs: def binomialInterval(n, k, alpha = 0.68):
      """
      Given n tests and k successes, return efficiency and confidence interval.
      """
      e = float(k)/n
      delta_e = 1/float(n) * np.sqrt(e * (1 - e) * float(n)) * alpha/0.68
      return e, [e - delta_e, e + delta_e]