A country's TFR drops from 2.5 to 1.6 over a decade, while completed fertility for cohorts passing through their childbearing years during the same period remains at 2.1. What best explains this discrepancy?
AThe TFR data must be incorrect — it cannot diverge this much from completed fertility
BWomen are postponing childbearing to later ages, creating a tempo distortion that depresses the period TFR below the cohort's actual completed fertility
CImmigration of childless women inflates the denominator without adding births
DReplacement-level fertility has changed due to declining mortality, making 1.6 the new replacement level
This is a classic tempo effect. When women delay childbearing — for example, shifting the mean age at first birth from 25 to 30 — period ASFRs at younger ages decline before ASFRs at older ages have fully compensated. The TFR, which sums current ASFRs across all ages, captures this temporary depression. Completed cohort fertility, measured after women finish childbearing, shows the actual quantum. Bongaarts and Feeney developed tempo-adjusted TFR (TFR*) to correct for this distortion.
Question 2 True / False
Replacement-level fertility is exactly 2.0 children per woman because each couple needs to produce two children to replace themselves.
TTrue
FFalse
Answer: False
Replacement level is approximately 2.1 in low-mortality settings, not 2.0, for two reasons: the sex ratio at birth is slightly above 1 (about 105 boys per 100 girls), so slightly more than 2 births are needed to produce one surviving daughter per woman; and some females die before completing their childbearing years. In high-mortality populations, replacement-level TFR can be 2.5 or higher because more women die before or during their reproductive years.
Question 3 Short Answer
Explain the difference between the gross reproduction rate (GRR) and the net reproduction rate (NRR), and what an NRR of exactly 1.0 signifies.
Think about your answer, then reveal below.
Model answer: GRR is the TFR counting only female births — the average number of daughters a woman would bear at current age-specific fertility rates, ignoring mortality. NRR adjusts GRR for the probability of surviving to each childbearing age, giving the average number of daughters a woman will bear who survive to reproduce. An NRR of exactly 1.0 means each generation of women is exactly replacing itself — one surviving daughter per woman — indicating zero long-term natural population growth in the absence of mortality change.
NRR is the more meaningful measure for long-term population replacement because it accounts for mortality. A population with high fertility but high female mortality could have a high GRR but an NRR near or below 1.0. NRR connects directly to stable population theory: when NRR = 1 and age-specific rates are constant, the population will eventually reach a stationary state with zero growth.