1. Charlton, J., Hartley, R., & Holland, W. (1983). Geographical variation in mortality from conditions amenable to medical intervention in England and Wales. Lancet, 8326, 691–696. doi: 10.1016/S0140-6736(83)91981-5 .
2. Cutler, D., Richardson, E., Keeler, T., & Staiger, D. (1997). Measuring the health of the US population. Brookings Papers on Economic Activity, 28, 217–282.
3. Dempster, A., Laird, N., & Rubin, D. (1977). Maximum likelihood from incomplete data via the EM algorithm. Journal of the Royal Statistical Society: Series B, 39, 1–38.
4. Green, W. (2003). Econometric analysis. Upper Saddle River, New Jersey: Prentice Hall.
5. Hair, J., Anderson, R., Tatham, R., & Black, W. (1998). Multivariate data analysis. Upper Saddle River, New Jersey: Prentice Hall.