8.1.3—Population dynamics metrics

Each population metric answers a different question: TFR describes births per woman, life expectancy describes expected years, natural increase compares birth and death rates, and doubling time estimates growth speed.

Use doubling time ≈ 70 ÷ growth rate (%) only after converting the growth rate to a percentage. Use natural increase = birth rate − death rate; if rates are per 1,000, divide the result by 10 to express a percent.

At 2% annual growth, doubling time is about 35 years; birth rate 30 and death rate 10 per 1,000 gives natural increase 20 per 1,000, or 2%.

Doubling time, not life expectancy or TFR; use 70 ÷ percentage growth.

Do not put a per-1,000 rate directly into 70 ÷ r; the formula expects percent units.