July 25, 2003

The Demographic Transition

The shape of the demographic transition since 1820. Population growth rates plotted as a function of (log) levels of real GDP per capita (measured in Maddison's 1990 "International Dollars". Data points are regions of the world since 1820 for six irregular (but sensible) subperiods. Trend line is a nine-point centered moving average of region-period points ranked by per capita income. To help with the scale, remember that a log of 6 corresponds to GDP per capita levels of $400 per year, that a log of 7 corresponds to $1100 per year, and 8, 9, and 10 correspond to $3,000, $8,100, and $22,000, respectively.

The figure shows how population growth rises rapidly as societies progress and grow their incomes from a Malthusian near-subsistence level of $400 (1990 International Dollars) per person per year up to $1,100 or so. Then population growth levels off--typically at 1.75% per year or so--as fertility restriction becomes widespread. Once societies pass $4,000 per capita a year or so, population growth rates start to decline markedly.

Of course, we don't really know what happens once incomes pass $25,000 per capita per year or so, or indeed if there will continue to be a systematic relationship at all.

Underlying data source: Angus Maddison (2001), The World Economy in Millennial Perspective (Paris: OECD).

Raw preliminary spreadsheet at: http://www.j-bradford-delong.net/movable_type/data-TCEH/Maddison_Millennial_Numbers.xls.

Other readings of interest include: Ronald Lee and Michael Anderson (2001) Malthus in State Space: Macro Economic-Demographic Relations in English History, 1540 to 1870, Journal of Population Economics, v.15, n.2. pp. 195-220. (Acrobat.pdf file)

Posted by DeLong at July 25, 2003 08:44 PM | TrackBack

Comments

"Of course, we don't really know what happens once incomes pass $25,000 per capita per year or so, or indeed if there will continue to be a systematic relationship at all." - Perhaps not, but we can get a good hint from comparing fertility in high to low income households. Fertility decreases with household income, at least in Sweden, with GDP/head of approx 25k USD.

Super-linear payoff from time spent at work/in school, which is typical for competence-based market economies, makes it costly both economically, but also in terms of social status, to have many kids. Advanced economies depend on immigrants from less advanced such.

Posted by: Mats on July 26, 2003 12:44 PM
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