Individual investors are the primary owners of these funds as opposed to institutions.
Institutions such as mutual funds don't buy shares of closed-end funds or other mutual funds because their customers don't like the idea of paying two sets of fees,.
We can postulate that individual investors would be more flighty than professional investors, such as pension funds and endowments, and thus, they would be subject to shifting moods of optimism or pessimism ("investor sentiment").
When individual investors are feeling perky, discount on closed-end funds shrink and when they get depressed or scared, the discounts get bigger.
Individual investors are also more likely than institutional investors to own shares of small companies.
Institutions shy away from the shares of small companies because these shares do not trade enough to provide liquidity a big investor needs.
How to measure individual investor sentiment?
So, if the investor sentiment of individuals varies, it would show up both in the discounts on closed-end funds and on the relative performance of small companies versus big companies.
That is exactly what was found. The average discount on closed-end funds was correlated with the difference in returns between small and large company stocks; the greater the discount, the larger the difference in returns between those two types of stocks.
How to profit from this investor sentiment variability?
The strategy of buying the closed-end funds with the biggest discounts earned superior returns (a strategy also advocated by Benjamin Graham). Burton Malkiel, author of A Random Walk Down Wall Street, has also advocated such a strategy.