docs: def deriv2(self,p):
          '''
          Second derivative of the negative binomial link function.
  
          Parameters
          ----------
          p : array-like
              Mean parameters
  
          Returns
          -------
          g''(p) : array
              The second derivative of the negative binomial transform link
              function
  
          Notes
          -----
          g''(x) = -(1+2*alpha*x)/(x+alpha*x^2)^2
          '''
          numer = -(1 + 2 * self.alpha * p)
          denom = (p + self.alpha * p**2)**2
          return numer / denom