The second model is:- Log(crh)= b0 + b1*time + b2*hvinf + b3*(time*hvinf). I can get similar prediction equations as above. In both these models, the intercept and the coefficient for time are same ie, b0 and b1 is same in both the regression models. In both the above regression models, I included a quadratic term for time, modifying the models as given below: Model-1: Log(crh)= b0 + b1*time + b2*time^2 + b3*hvptb + b4*(time*hvptb). Model-2: Log(crh)= b0 + b1*time + b2*time^2 + b3*hvinf + b4*(time*hvinf). On estimating the models I find that the values of b0 and b1 are not the same for the two models. Hence the prediction equation for the normal people are different in the two models. Also, this is the simplified version of the problem. I intend to estimate the two models using gllamm. I’d appreciate it if anybody can shed some light on this issue. Thanks, Leny Leny Mathew Data Analyst Division of Perinatal Research Department of Obstetrics/Gynecology Drexel University College of Medicine 245 N. 15th Street, 17th Floor Mail Stop 495 Philadelphia, PA 19102 Phone: 215-762-2069 * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/