America news discusses how the CIA and other agencies go about forecasting the physical and mental health of foreign leaders. It is not clear from the article how forecasts are derived from the intelligence gathered, or how accurate the forecasts are. Be warned: Information in the article on some data collection methods may upset senstitive readers.
The Forecasting Principles site summarizes all useful knowledge about forecasting so that it can be used by researchers, practitioners, and educators. The site is devoted to improving decision making by furthering scientific forecasting.