Explanations for fluctuations in fertility
Fertility follows some long-term trends, but there are also minor year-to-year fluctuations. This page explains the possible sources of fluctuations.
There are some obvious culprits:
- Definitional ambiguity
- Random variation
- Measurement error
We discuss factors that cannot be reduced to these ones.
Superstitions associated with specific years
This phenomenon operates particularly in East and South-East Asia: some years are considered very lucky for having babies, whereas some years are considered very unlucky for having babies.
Examples:
| Year | Country | Fertility information | Considered auspicious or inauspicious? | TFR two years before | TFR one year before | TFR that year | TFR next year | TFR two years later | TFR source |
|---|---|---|---|---|---|---|---|---|---|
| 1966 | Japan | fertility in Japan | inauspicious | 2.045 | 2.145 | 1.579 | 2.224 | 2.127 | Human Fertility Database for all years |
| 1988 | Singapore | fertility in Singapore | auspicious (Dragon Year) | 1.43 | 1.62 | 1.96 | 1.75 | 1.83 | UN data compiled by Gapminder for all years |
| 2000 | Singapore | fertility in Singapore | auspicious (Dragon Year) | 1.48 | 1.47 | 1.6 | 1.41 | 1.37 | UN data compiled by Gapminder for all years |
| 2010 | Taiwan | fertility in Taiwan | inauspicious | 1.05 1.05 |
1.022 1.03 |
0.887 0.895 |
N/A 1.065 |
N/A 1.265 |
First row is Human Fertility Database data, second row is UN data compiled by Gapminder. HFD data goes only till 2010. |
| 2012 | Singapore | fertility in Singapore | auspicious (Dragon Year) | 1.261 | 1.267 | 1.275 | N/A | N/A | UN data compiled by Gapminder for all years |
| 2012 | Taiwan | fertility in Taiwan | auspicious | 0.895 | 1.065 | 1.265 | N/A | N/A | UN data compiled by Gapminder for all years |
Economic fluctuations
Year-to-year fluctuations in economic performance can lead to fluctuations in fertility rates. In general, years of economic depression are accompanied by lowe fertility rates, and the boom years are accompanied by higher fertility rates. The effect is largely temporary and involves a relative assessement of economic conditions at present and in the near future, rather than an assessment of the absolute state of the economy. In other words, people are choosing to delay having children rather than to have fewer children.
Short-run response to government policies
In some cases, fertility may grow a lot in years when governments announce pro-natalist policies, as people try to take advantage of the policies. Some of this may be a stable long-term change. However, there are also often one-time fluctuations as a result of the policy. The reason is that people choose to speed up having births they might otherwise have delayed for later, with the specific goal of taking advantage of the government policy. This is expected to be most significant in cases where the policy itself is known or suspected to be temporary.