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“Total Market” Investing and Multi-Factor Models

A reader writes in, asking:

“I would like to ask you about factor investing. For background, I am a plain vanilla investor. I use the Vanguard Market-cap weighted Total World Stock fund. As simple as it gets!

However I have been reading literature about the case for factor investing. There seems to be a broad consensus that multi-factor models explain returns much better than the CAPM. [Mike’s note: the Capital Asset Pricing Model is an older model in finance that states that a portfolio’s expected return is a function of how sensitive the portfolio is to market risk. More recently, various multi-factor models have said that a portfolio’s expected return also depends on other things, such as how much of the portfolio is allocated to small-cap stocks (as opposed to large-cap stocks) or to value stocks (as opposed to growth stocks).]

I have heard many recommending tilting to small and value stocks.

Do I need to be concerned about my plain vanilla strategy? Am I potentially missing out on much superior returns over the long run?”

It’s true that there is, roughly, a consensus that multi-factor models explain returns better than CAPM. That isn’t an argument for or against a “total market” portfolio though.

To back up a step, a one-factor model such as CAPM tells us that stocks are riskier than bonds and should therefore usually have higher returns. But that’s not an argument for an all-stock portfolio (or any other particular stock/bond allocation). It all depends on your own personal balance of desire for return and willingness to take stock market risk.

Similarly, in multi-factor models, value stocks and small-cap stocks are generally considered to have higher risk and higher expected return than their counterparts. But that’s not an argument for any particular value/growth allocation or small/mid/large allocation. Again it all depends on your personal balance of desire for return and willingness to take risk.

In my experience, it’s usually the salespeople (e.g., certain advisors or purveyors of mutual funds) who argue that a given allocation is better, while the academics are much more neutral on the matter. For instance, Eugene Fama (one of the two people originally behind multi-factor research) was super clear in a video interview on Dimensional Fund Advisors’ website. The video disappeared when they restructured their site a few years back, but here’s the relevant quote:

Interviewer: Some people cite your research showing that value and small firms have higher average returns over time and they assume that you would recommend most investors have a big helping of small and value stocks in their portfolios. Is that a fair representation of your views?

Fama: Um, no. (Laughs) Basically this is a risk story the way we tell it, so there is no optimal portfolio. The way I like to talk about it when I give presentations for DFA or other people is, in every asset pricing model, the market portfolio is always an efficient portfolio. It’s always a relevant portfolio for an investor to hold. And investors can decide to tilt away from that based on their personal tastes.

But that’s what it amounts to. You can decide to tilt toward more value or smaller size based on your tastes for these dimensions of risk. But you needn’t do it. You could also decide to go the other way. You could look at the premiums and say, no, I think I like the growth stocks better. Then, as long as you get a diversified portfolio of them, I can’t argue with that either.

So there’s a whole multi-dimensional continuum here of efficient portfolios that anybody can decide to buy that I can’t quarrel with. And I have no recommendations about it because I think it’s totally a matter of taste. If you eat oranges and I eat apples I can’t really quarrel very much with that.

As far as still-available interviews with Eugene Fama, here are two:

In the first video, Fama talks about the origin of the 3-factor model. While he doesn’t explicitly get around to portfolio construction in this interview, he does state very clearly that his view is that the higher returns are the result of higher risk. (Around 5:26 is where the conversation leads to this point.)

The second video is longer and covers a lot of topics. The video’s publisher explicitly requests that it not be quoted, so I won’t quote it. Instead, I’ll just point out that around 28:45, Fama says things very similar to the interview that I quoted above. And at 35:28 he says something very clear about holding a market portfolio and whether he thinks it’s a good choice or not.

In my view, overweighting small-cap stocks or value stocks in your portfolio is a perfectly reasonable thing to do. But on occasion you’ll encounter people who indicate that doing so is the smart way to invest and only an uninformed investor would say otherwise. But that’s clearly not true.

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