Additional information on finite mixture        models for count data and a similar example are found in       Deb, P. and P. K. Trivedi, 1997, Demand for medical care by the       elderly: A finite mixture approach, _Journal of Applied Econometrics_,       vol. 12, 313--336.
Data is analyzed in Cameron, A. C. and P. K. Trivedi, 2010,        _Microeconometrics Using Stata, Rev. Ed., College Station,        TX: Stata Press.
Data on annual number of doctor visits for individuals age 65 and older       from the U.S. Medical Expenditure Panel Survey for 2003.