Thursday, March 28, 2019

Declining Fertility Rate Hysteria Is A Misrepresentation of Statistics

One thing I have begun to notice more of late is fear mongering about declining birth rates, especially by white nationalists and conservatives, but occasionally the centre-left will partake in it. An article in Pacific Standard magazine summarizes this very well. The article cites a total national fertility rate, for the U.S., as 1.765.5 births per 1,000 women of child bearing age, which is about 1.76 births per woman of child bearing age. Since this is below the benchmark replacement level of 2,100 births per 1,000 women of child bearing age, or 2.1 births per woman of child bearing age, the author concludes that we will have a smaller work force in the future, assuming the downward trend continues, and consequently fewer people will be paying into social security (Wheeling, 2019). However, the CDC study cited in the article does not support this conclusion; in fact, the conclusion is based on a bad misinterpretation of total fertility rate. Total fertility rates are estimations of how many births a hypothetical group of 1,000 women would have if the age specific birth rates in a given year remained constant over their reproductive years; total fertility rate is calculated by adding all 5 year age-specific birth rates and multiplying the sum by 5 (Mathews & Hamilton, 2019). Since this statistic assumes that women's current age specific birth rates will remain constant over their reproductive years it is only an estimate of possible final fertility at the end of their reproductive years (Mathews & Hamilton, 2019). Final fertility is contingent on women's actual age-specific birth rates, rather than a hypothetical continuation of current age specific birth rates, during their reproductive years (Mathews & Hamilton, 2019). It is not conclusive that all women will end their reproductive years with an average of 1.76 births. It is also important to consider that the total fertility rate is calculated for all women of reproductive age, which includes all females between 15 and 44 years of age. Within such a large cohort there's inevitably going to be a lot of zeros that will pull down the mean, especially for females between 15 and 24 years of age who are usually still in school. The article also notes that the average age for first marriage has risen to 27 years of age, but fails to see the obvious implication for declining total fertility rates: that a there may be, as a result of delayed marriage, a lot more women with 0 births before age 27 than after age 27. Therefore, the mean may not be the best indicator of how many children women will have, just as it would not be a good indicator of the income of bar patrons if Bill Gates walked into that bar.

References

Mathews, T., & Hamilton, B. E. (2019). Total fertility rates by state and race and hispanic origin: United States, 2017. National Vital Statistics Reports, 68(1), 2-5.
Wheeling, K. (2019, January 11). The U.S. Birth Rate Is Still Falling. Retrieved March 26, 2019, from https://psmag.com/news/the-us-birth-rate-is-still-falling

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