There has already been much ink, and maybe even some blood, spilled debating the merits of “Active Share” for judging an investment fund. There was the original paper, a critique of that paper written by some of my colleagues, a reasonable (which doesn’t mean I agree with it) response to AQR’s piece, and even a seriously deranged1 response to my colleagues’ work (thankfully I’m known for a certain aplomb and even sangfroid in such tense situations and have helped calm everyone down). I don’t seek to re-open this debate but, rather, to focus on one aspect of it. Admittedly it’s an aspect near and dear to my heart and wallet. I believe (hope) this aspect of the debate is so clear that all sides can agree. Active Share may or may not make sense for judging traditional active discretionary stock pickers (and when I say “make sense” I mean on its own and versus other measures such as tracking error). However, Active Share clearly makes no sense, and is, in spirit, explicitly backwards for judging direct factor investors (or quantitative investors, or smart beta investors, or style investors, or structured investors; all of which I consider near synonyms with different marketing labels — I haven’t even come very close to covering all the possible options so let the semantic wars rage on!).
Here’s a brief and probably insufficient review. Having a metric to judge how much long-only active portfolios differ from their benchmarks is clearly useful. While obviously useful to know how much relative risk one is taking, it’s also particularly useful for judging the value proposition of such an investment. That is, paying a lot in fees for small deviations (closet indexing) is probably a bad idea. The proponents of Active Share argue that besides detecting closet indexing it’s also a good metric for judging these managers’ average skill and a better metric than some other possible candidates. That is a bit different and goes further. They’re saying higher Active Share (bigger bets vs. the index on the Active Share scale) is, on average, also indicative of delivering more alpha (with all the difficulties judging “alpha” can present) and other major alternatives not as useful.
Explicitly or implicitly Active Share is, and must always be, judged against alternative methods of making similar judgments. The most prominent alternative is “tracking error.” Active Share essentially doesn’t use statistics. It simply adds up the size of the active managers’ deviations from the index without regard for whether they’re making an active bet in a volatile stock versus doing so in a calm stock, or whether many or few of their active bets are highly correlated with one another. For instance, if an active manager took ten separate stock bets all the same dollar size and each bet was overweighting stocks in the same industry, tracking error would invariably say this is riskier (a bigger active bet) than if the stocks were all in very different industries (a more diversified and thus lower tracking error bet). In contrast, Active Share is indifferent and would report the same result either way. You can make an argument for either tracking error or Active Share (and the linked papers above certainly do!). Active Share has the virtue, and perhaps handicap, of great simplicity where tracking error perhaps has the negative of being dependent on estimates of the volatilities and correlations among stocks (that is, two different analysts calculating Active Share will usually come up with the same number while this is not necessarily true for tracking error2). I think it’s pretty clear, at least in this and in similar examples, that tracking error is a better estimate of the risk taken versus the benchmark (ignoring the correlation and volatility of bets, even if measured imperfectly, seems pretty serious for estimating risk). That would, presumably, not surprise Active Share proponents as it’s not their main goal. Where it gets interesting is evaluating claims that one or the other measure also tells us where manager skill is likely to exist.
Now why would Active Share be better than tracking error as a proxy for manager conviction and therefore, perhaps, manager skill?3 For instance, it may be the case that managers are really good at one part of what they do (e.g., picking stocks within industries to continue with that example) but really bad at other things (e.g., picking industries4) so, in this hypothetical case, if higher tracking error comes from industry concentration it is actually not more value for the fee dollar but just risk without reward. In this case, tracking error may be the better estimate of the actual risk taken (again you’d certainly hope so) but not a better measure of where skill or value-added comes from. Shocking to no one, I tend to side with AQR’s arguments that cast doubt on Active Share’s ability to forecast where skills lies (in the absolute and relative to tracking error). But, I do think there are reasonable points and arguments on both sides and the debate should continue (sans the most seriously deranged contributions).
[drizzle]All that brings us to my real point (I had you worried I wouldn’t get there, right?). Direct factor investing (or any of its near synonyms) is a different ball game from traditional active stock picking. Specifically, Active Share, in particular when compared with tracking error, makes little to no sense for direct intentional factor tilted long only portfolios. These portfolios aren’t just different on the surface from traditional active stock picking. They are different in a far deeper way. They are only about getting exposure to the desired factor or factors while taking as little other exposures as possible (in this essay I always mean exposure as versus the index — the same exposure/risk that Active Share and tracking error deal with). That entails minimizing exposure to unwanted factors (everything but the desired factor or factors) and maximizing exposure to desired ones (the desired factor or factors). Perhaps most importantly, it implicitly entails taking as little specific stock risk as possible while pursuing the earlier goals (the “right” factor exposure). For instance, a running issue in my life is, when questioned by the media, sometimes, even after we explicitly ask them not to, I still get asked “what’s your favorite stock?” I usually respond, often to an incredulous questioner who looks at me like I’m just a little slow or addled, “I don’t know” (truth be told I say that even if I do know as it’s kind of fun and lets me go on to make the bigger point).
Put another way, an imperfect yet useful way to think of factor or smart beta investing is an attempt, relative to the index, to bet on the factor or factors you believe in, not bet on those you don’t, while otherwise implicitly minimizing Active Share.5 One can like or dislike these products (shockingly, please put me mostly in the “pro” camp) but it seems really odd to judge them on whether they have enough Active Share when minimizing Active Share is a