GWWC says 4.8% per year attrition. If we say the OP data is half life of 5 years and exponential decay, that is 13% attrition per year. That would mean an expected duration of being an EA of eight years. I think I remember reading somewhere that GWWC was only assuming three years of donations, so eight years sounds a lot better to me. Another thought is that the pledge has been compared with marriage, so we could look at the average duration of the marriage. When I looked into this, it appeared to be fairly bimodal, with many ending relatively quickly, but many ending till death do they part. GWWC argues that consistent exponential decay would be too pessimistic. If we believe the 13% per year attrition, that means we need to recruit 13% more people each year just to stay the same size.
GWWC says 4.8% per year attrition. If we say the OP data is half life of 5 years and exponential decay, that is 13% attrition per year. That would mean an expected duration of being an EA of eight years. I think I remember reading somewhere that GWWC was only assuming three years of donations, so eight years sounds a lot better to me. Another thought is that the pledge has been compared with marriage, so we could look at the average duration of the marriage. When I looked into this, it appeared to be fairly bimodal, with many ending relatively quickly, but many ending till death do they part. GWWC argues that consistent exponential decay would be too pessimistic. If we believe the 13% per year attrition, that means we need to recruit 13% more people each year just to stay the same size.