Keyfitz Momentum Factor Calculator
Evaluate the Keyfitz (1971) approximate population-growth momentum factor M = b e0 (1 - exp(-r mu)) / (r mu), the ratio by which a stable growing population would still grow after fertility instantly drops to replacement.
Description
Evaluate the Keyfitz (1971) approximate population-growth momentum factor M = b e0 (1 - exp(-r mu)) / (r mu), the ratio by which a stable growing population would still grow after fertility instantly drops to replacement.
Evaluate the Keyfitz (1971) approximate population-growth momentum factor M = b e0 (1 - exp(-r mu)) / (r mu), the ratio by which a stable growing population would still grow after fertility instantly drops to replacement.1
When to use Keyfitz Momentum Factor Calculator
Use this stable-population relationship for analytical schedules whose fertility, mortality, migration assumptions, and age intervals match the model.
- Birth rate b
- Stable-population annual birth rate b.
- e0
- Life expectancy at birth e0 in years.
- Growth rate r
- Stable annual growth rate r (may be negative).
- mu
- Mean age of childbearing mu in years.
How the method works
- Momentum
- Momentum factor M; above one signals continued growth after replacement fertility.
Limitations and assumptions
Stable-population identities assume fixed vital rates and usually a closed population. Real populations with changing schedules or migration may be far from the implied equilibrium.
Alternative or Complementary measures
Compare the stable-population result with an observed age distribution or a cohort-component model using changing schedules. The difference indicates how strongly the equilibrium assumption shapes the result.
References
-
Euler–Lotka equation — Wikipedia contributors
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