As rates have risen, investors have, once again, started asking the perennial question: Is the bond bull market over and are rates normalizing? In thinking about bond yields, it is important to keep longer-term factors in mind that have nothing to do with central bank policy. Low yields have correlated with two, related longer-term trends: low nominal GDP (NGDP) and an aging population. The reason they’re related is that an aging population means slower growth in the workforce, and in turn, slower economic growth.
An aging population impacts rates through a second mechanism. As consumers age, their borrowing and investing patterns shift. Older households tend to borrow less and demonstrate a preference for income, in the process raising the demand and lowering the supply of bonds. The net result is that older populations tend to be associated with lower real, or inflation-adjused interest rates. This dynamic has been at work for decades and helps explain why low yields predated the financial crisis.
Because the population will not get younger any time soon, what would need to change to push rates back to “normal”? In terms of the real economy, the simple answer is faster nominal growth. Looking back over the past 60 years, the level of nominal growth has been the key to understanding the level of rates. During this period, a smoothed average of nominal growth explains almost 60% of the variation in long-term rates (see the chart below).