1. Cameron AC, Trivedi PK (1998) Regression Analysis of Count Data. Cambridge Univ. Press, NY, USA.
2. Casella G, Berger R (2002) Statistical Inference. (2nd edn), Thomson Learning, Pacific Grove, CA, USA.
3. Tiku ML, Vaughan DC (1997) Logistic and nonlogistic density functions in binary regression with nonstochastic covariates. Biometrical Journal 39(8): 883-898.
4. The generalized secant hyperbolic distribution and its properties;Vaughan;Communications in Statistics - Theory and Methods 31(2),2002
5. Evaluation of the maximum likelihood estimator when the likelihood equation has multiple roots;Barnett;Biometrika 53(1),1966