The leaving is far more important than the disfellowshipped, dear slimboyfat. And the calculation is very accurate and close to reality.
I think it's the only way to know how many people are leaving the WT. And if you believe the figures given by the WT (1%), you believe in Santa Claus.
By the way, theses figures has been confirmed officialy by the Bethel of France (in 2005) when a Minister of the French gouvernment asked if they were true . They said 'yes, we have something like that" and they used these figures to prove that they are not a sect and they let people to leave the WT freely.
These calculation has been done by an ex-JW who worked for the French government (MILIVUDES). He's my friend too by the way. So I picked up the method.
About the death rate : JW are part of the population and like it the JW people assumes to have the same death rate. Without officialy DR, you have to take from the area you live (it's different between England & France, France & Belgium, etc...). There is no reason to not apply statistics for JW when you use it for other religion. Logical, no ?