A large body of research in psychology and economics shows that human beings tend to form their expectations by relying on past experiences—especially recent ones. Malmendier and Nagel (2011), for instance, talk about investors who live through long periods of poor stock market performance and how this experience affects their risk-taking propensities… for life. The most famous example comes from the “Depression Babies,” an entire generation that was scarred for life by the financial and macroeconomic shocks of the Great Depression. Of course the opposite effect also exists: periods of economic ebullience give rise to more intrepid investors, entrepreneurs, and so on.

Those times might feel like a distant past now, but until recently 3–4% growth in real GDP was considered “normal.” So it should come as no surprise that the economic performance of the past few decades has strongly influenced expectations about economic growth. However, when optimistic expectations get detached from reality we risk creating a significant expectations gap—a disconnect between what we take for granted given our recent experiences and what we should anticipate given simple arithmetic.

We explore the role of demography—one of the three Ds of the 3-D hurricane of debt, deficits, and demographics—on economic growth in this issue of Fundamentals. The following synopsis of our forthcoming paper on the topic (Arnott and Chaves, 2013) demonstrates that favorable trends in the size and composition of populations have helped to fuel the rapid economic growth experienced in the developed world over the past 60 years, and their reversal plays a crucial part in the current rapid deceleration in developed world growth.

Demographic profile

Demographic Evolution

Tracing very long term trends will certainly help situate existing and emerging demographic states of affairs in their historical context. It may also indicate what used to be “normal,” if, indeed, there ever was such a condition. We examine four distinct phases that represent past, current, and future population profiles across different countries:

Demographic Evolution Phase I. The first phase, covering most of human history, was ostensibly a high-mortality steady state, with births roughly matching deaths, short lifespans, and elevated support ratios (the number of non-workers, young and old, supported by the labor force). Life in the first phase can probably be described best by Hobbes’ famous quote as “solitary, poor, nasty, brutish, and short.”

Demographic Evolution Phase II. This phase, beginning around the time of the industrial revolution and climbing to a pinnacle in the decades after the Second World War, was characterized by a steady rise in life expectancy and a decline in birthrates. The working-age population soared and support ratios improved enormously.

Demographic Evolution Phase III. This phase, beginning in the present century, is almost an inverted image of the second phase: the fraction of seniors skyrockets and the fraction of workers tumbles. Until fertility rates get back to replacement levels (roughly 2.1 children per woman of child-bearing age), the population crests and begins to subside, with very high support ratios associated with senior citizens. However, this should not come as a surprise, because both phases II and III are impelled by the same forces: rising life expectancies and falling fertility rates.

Demographic Evolution Phase IV. This phase is the “future state,” which is by definition somewhat speculative. For convenience, we model it as a new steady state with births equaling deaths, and with long lifespans, perhaps much longer than today’s. We include it for the purpose of comparison; since phases II and III are unquestionably temporary, it must differ from them.

By Rob Arnott Via mauldineconomics