Loss aversion is a basic tenet of behavioural finance, particularly prospect theory. It says that people are averse to losses and become risk seeking when confronted with certain losses. There is a huge amount of experimental evidence in support of loss aversion, and Daniel Kahneman won the Nobel Prize in Economics mainly for his work in prospect theory.
What are the implications of prospect theory for an economy with pervasive negative interest rates? As I write, German bund yields are negative up to a maturity of five years. Swiss yields are negative out to eight years (until a few days back, it was negative even at the ten year maturity). France, Denmark, Belgium and Netherlands also have negative yields out to at least three years.
A negative interest rate represents a certain loss to the investor. If loss aversion is as pervasive in the real world as it is in the laboratory, then investors should be willing to accept an even more negative expected return in risky assets if these risky assets offer a good chance of avoiding the certain loss. For example, if the expected return on stocks is -1.5% with a volatility of 15%, then there is a 41% chance that the stock market return is positive over a five year horizon (assuming a normal distribution). If the interest rate is -0.5%, a person with sufficiently strong loss aversion would prefer the 59% chance of loss in the stock market to the 100% chance of loss in the bond market. Note that this is the case even though the expected return on stocks in this example is less than that on bonds. As loss averse investors flee from bonds to stocks, the expected return on stocks should fall and we should have a negative equity risk premium. If there are any neo-classical investors in the economy who do not conform to prospect theory, they would of course see this as a bubble in the equity market; but if laboratory evidence extends to the real world, there would not be many of them.
The second consequence would be that we would see a flipping of the investor clientele in equity and bond markets. Before rates went negative, the bond market would have been dominated by the most loss averse investors. These highly loss averse investors should be the first to flee to the stock markets. At the same time, it should be the least loss averse investors who would be tempted by the higher expected return on bonds (-0.5%) than on stocks (-1.5%) and would move into bonds overcoming their (relatively low) loss aversion. During the regime of positive interest rates and positive equity risk premium, the investors with low loss aversion would all have been in the equity market, but they would now all switch to bonds. This is the flipping that we would observe: those who used to be in equities will now be in bonds, and those who used to be in bonds will now be in equities.
This predicted flipping is a testable hypothesis. Examination of the investor clienteles in equity and bond markets before and after a transition to negative interest rates will allow us to test whether prospect theory has observable macro consequences.