If Rube Goldberg had been a portfolio manager, instead of a cartoonist renowned for designing comically complicated machines for accomplishing simple tasks, he might have specialized in long-short equity funds.

These funds use a mix of positions, owning some stocks in the hope that their prices will rise and holding others “short” — borrowing shares and selling them in the hope that their prices will fall. The funds also may use derivative instruments like stock index futures.

Long-short funds might be particularly appealing now that trading is so volatile and prices are moving up and down instead of up and up. But with all that buying and selling, the average long-short fund barely broke even over the 12 months through June, according to Morningstar, and returns over five years are only marginally better than those of bank deposits or short-term bond funds.

Financial planners attribute the persistent weakness to a mix of financial and market factors. Some hold out hope that returns will improve when conditions change, flipping the influence of those factors from negative to positive. Others maintain that the inherent complexity and expense of long-short funds ensures that they will remain poor investments. What everyone seems to agree on is that they have failed for many years to enhance or protect portfolios.