the leg you can actually buy

A friend forwarded a smart-beta value fund last week. The pitch leaned on the value premium from the textbooks, something like five points a year over the market across decades of data. His fund had done maybe three points over the index, and he was ready to sell it for underperforming.

I told him to stop. He hadn't bought a bad fund. He'd bought one leg of a two-legged trade.

Here is the part the brochure skips. Every factor premium in the academic literature is a long-short spread. You go long the cheap stocks and short the expensive ones. Long the small, short the large. Long the recent winners, short the recent losers. The premium is the distance between those two baskets, not the return of either one on its own.

A plain mutual fund or a smart-beta index fund can't short anything. So it owns the long leg and leaves the short leg on the table. And how much of the premium actually lives on the long side depends entirely on the factor. The long leg keeps almost all of the size premium, around 60 percent of value, and only about half of momentum (Israel and Moskowitz, 2013). Same word, three very different trips from the paper to your portfolio.

Then there is the quieter problem. Whatever the long leg keeps still arrives wrapped in full market beta. A long-only value fund is the index plus a tilt, not the value premium standing alone. Strip the beta and the tilt is smaller than the sticker.

None of this makes factor funds bad. It just means you should know which leg you are buying and how much of the premium survives before you pay an active fee for it. Two or three points of genuine tilt over the index is worth having. Paying a long-short price for a long-only slice is not.

Pull the factors apart before you tilt: