The Marriage of Grossman-Stiglitz and Dunning-Kruger

February 7th, 2021 by Potato

With passive index investing, there’s a bit of a concern from some corners that if too many people become indexers, then there won’t be anyone to do security analysis. The market will stop being efficient, and the free ride that passive investors enjoy will be over. While it’s a “paradox” in that passive investing only works if there are active investors to make the market efficient, in practice, most of us aren’t too worried about it — there will always be some active investors to help determine prices.

I’ve seen the argument (not that I can find it now to link to it) that the weakest active managers will be forced out first (the ones who were basically closet indexers but charging 2.4% for the privilege). The remaining good managers may make some pre-fee alpha, and help keep prices rational for the passive investors. So as active managers continue to broadly under-perform index funds net of fees, and more investors move to passive funds, the ones who were least able to generate alpha will be the ones forced out of the industry.

But watching the chaos of the markets over the last little while, I also remembered the Dunning-Kruger effect: those who are least skilled are also not generally able to accurately assess their skill. So as passive continues to prove to be a good strategy, the ones who don’t switch are not just the most skilled (still generating alpha) but also the least (who may not know the risks they take or that they’re not generating alpha). And professional managers are not the only ones in the market — there are a lot of retail traders out there. On the whole they’re dwarfed by institutional money, but they can certainly move a few sectors and specific names. And so they have.

And social media in some ways fuels it — most people would never trade on a tip made in a video, tweet, or forum post. But the world’s a big place, and there are lots of people who do. And the algorithms are good at serving up more and more of that if you engage with it.

The last little while has seen some market moves that are just plain hard to call “efficient”. The weak-form efficient market hypothesis still applies — no matter how crazy it is, it’s still unpredictable enough that you can’t reliably profit from it, so just stick with index funds. Looking at the Gamestonk run-up and crash, calling the top never looked like a sure enough bet that I wanted to do it. Tesla, a niche, money-losing maker of electric vehicles (with a money-losing solar panel division that’s shrunk significantly since its related-party bailout, I should add, before the comments section fills with wails that it is also “an energy company”) somehow became the world’s most valuable automaker. And if you tried to short it at the point that it passed Toyota, you got destroyed as it continued to go straight up and become the most valuable automaker by such a margin that it’s worth more than all the global brands you recognize combined.

But even then, you just have to look around and shake your head at the stuff people are buying. An electric — no, hydrogen! — truck company with no working trucks, no plan to make any, and an executive chairman who left in disgrace is worth $9B, with $500M in shares traded on a given day. Weed companies went up and up and up ahead of legalization in Canada, even as the sector became way bigger than the most optimistic projections of post-legalization market size, and you could not escape the hype. Space is a cool idea, but is Virgin Galactic really worth $13B (and 3X what it was a year ago?).

I’ve read a lot of stuff on active investing, and many articles make points about second-order, third-order thinking — how will the market react, what’s already priced in, etc. Lately it seems like that stuff will get you killed. There seems to be a lot of people in the meme trades, but there’s no way to go and become an active investor and profit from it: all I can do is rant on my blog about how crazy some of this stuff seems.

2 Responses to “The Marriage of Grossman-Stiglitz and Dunning-Kruger”

  1. Michael James Says:

    As always it’s way easier to identify stocks that are way over-valued than stocks that are way under-valued. The problem is that the market can crush a short-seller of over-valued stocks even if he is eventually right, but those who go long on under-valued stocks can wait indefinitely.

    I find it strange that there is so much more discussion of Tesla’s stock than their technology. The fact that the stock is way over-valued doesn’t concern me because I have no plane to own it (outside a bit in an index fund), but the technology fascinates me. Even better would be the technology of any company that eventually beats Tesla in sales of new technology.

  2. Potato Says:

    I’ve been following the technology for a while, and fascinating is one way to put it!

    The supercharger network was a legitimately brilliant idea to solve range anxiety, and now fast charging is pretty much standard (if not yet standardized) with other networks building out.

    But some of their technology/implementation is infuriating (esp. the over-promising on driver-assistance-that-maybe-one-day-will-be-automation-but-not-this-day).

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