TY  - JOUR
A1  - Cohen, Joel E.
T1  - Is the fraction of people ever born who are currently alive rising or falling?
Y1  - 2014/05/16
JF  - Demographic Research
JO  - Demographic Research
SN  - 1435-9871
SP  - 1561
EP  - 1570
DO  - 10.4054/DemRes.2014.30.56
VL  - S8
IS  - 56
UR  - https://www.demographic-research.org/special/8/56/
L1  - https://www.demographic-research.org/special/8/56/s8-56.pdf
L2  - https://www.demographic-research.org/special/8/56/s8-56.pdf
N2  - Background: Some journalists and demographers have asked: How many people have ever been born? What is the fraction F(t) of those ever born up to calendar year t who are alive at t? The conditions under which F(t) rises or falls appear never to have been analyzed. 

Objective: We determine under what conditions F(t) rises or falls. 

Methods: We analyze this question in the model-free context of current vital statistics and demographic estimates and in the context of several demographic models. 

Results: At present F(t) is very probably increasing. Stationary, declining, and exponentially growing population models are incapable of increasing F(t), but a doomsday model and a super-exponential model generate both increasing and decreasing F(t). 

Conclusions: If the world's human population reaches stationarity or declines, as many people expect within a century, the presently rising fraction of people ever born who are now alive will begin to fall. 

Comments: It is curious that nearly all empirical estimates of the number of people ever born assume exponential population growth, which cannot explain increasing F(t). 

ER  -