Thanks—I understand now. I thought $855 was the price SPY would reach if the current price increased by 50%. 

If you buy a $855 Strike price call for that date and SPY increases 50% by then you get a 12x return.

I never traded options, but isn’t the return you get critically sensitive on the date before expiration by which the strike price is hit? If this happens just before expiration, my understanding is that the option is worthless: there is no value in exercising an option to buy now at some price if that happens to be the market price. More generally, it makes a big difference whether the strike price is hit one week, one month, or one year before expiration.

Are you making any implicit assumptions in this regard? It would be useful if you could make your calculations explicit.

Mmh, if there is no reason to take that particular trader seriously, but just the mere fact that his trades were salient, I don’t see why one should experience any sense of failure whatsoever for not having paid more attention to him at the time.

Still, my main point was about the reasons for taking that particular trader seriously, not the sense of failure for not having done so, and it seems like there is no substantive disagreement there.

Why do you focus on this particular guy? Tens of thousands of traders were cumulatively betting billions of dollars in this market. All of these traders faced the same incentives.

Note that it is not enough to assume that willingness to bet more money makes a trader worth paying more attention to. You need the stronger assumption that willingness to bet n times more than each of n traders makes the single trader worth paying more attention to than all the other traders combined. I haven’t thought much about this, but the assumption seems false to me. 

Audible has just released an audio version of Nick Bostrom’s Deep Utopia.

I was delighted to learn that the audiobook is narrated by David Timson, the English actor whose narrations of The Life of Samuel Johnson and The Decline and Fall of the Roman Empire I had enjoyed so much. I wonder if this was pure chance or a deliberate decision by Bostrom (or his team).

pollsters will have attempted to correct mistakes, and if they knew that there would be an R/D bias this time, they'd adjust in the opposite way, hence the error must be unpredictable.

Exactly. Silver has discussed this dynamic in some of his old FiveThirtyEight articles. The key is to appreciate that polling error is not an effect one can naively predict by looking at past data, because it is mediated by polling agencies’ attempts to correct it.

Silver’s model and most other lines of evidence indicate that the US presidential race is as close to a tossup as it gets. But, as of this writing, you can buy Harris contracts on Polymarket for 38 cents. The explanation for this apparent mispricing seems to be that, over the past few days, a single pro-Trump trader has poured tens of millions of dollars into the platform. “Domer”, the author of the linked tweet and Polymarket’s most successful trader to date, claims that this effect has depressed Harris’s contract price by around five cents, though I am unable to independently confirm this claim.

There is an archived version here.

See also this comment by Gwern.

What are, in you assessment, some of the most cost-effective ways of throwing money at the problem of reducing existential risk?