Oh hello.

I knew Dr Rorabeck. He was a wonderful guy. @SchulichMedDent does have much to be proud of. Like any institution, it has its warts.

Survivorship Bias 101

History is written by the victors. But if we exclusively focus on these successes, we allow survivorship bias to distort our understanding of the world.

But what is "survivorship bias" and how does it work?

Here's Survivorship Bias 101!

👇👇👇

1/ First, a few definitions.

Survivorship bias is the logical error of concentrating on survivors (successes) and ignoring casualties (failures).

When we do so, we miss the true "base rates" of survival (the actual probability of success) and arrive at flawed conclusions.

2/ When we completely ignore failures, we lose our ability to correctly identify the differences between successes and failures.

Put simply, exclusively focusing on successes may actually inhibit our ability to identify (and replicate) the actions that led to such success.

3/ Cicero wrote on the topic over 2,000 years ago.

An atheist named Diagoras is shown portraits of people who prayed and were saved from death at sea as proof of God's existence.

Diagoras replies, "I see those who were saved, but where are those painted who were shipwrecked?"

4/ Cicero cuts right to the point - we cannot conclude that prayer led to being saved from the sea if we ignore those who prayed and then drowned.

Survivorship bias can lead to a deeply-flawed understanding of cause-and-effect relationships.

Let's look at some examples.

THREAD ON IRONFLY

These days the most preferred strategy for option sellers due to improved margins is IRONFLY. It's essentially a short straddle with long strangle. Long strangle acting as 'WINGS', which help in capping the unlimited risk associated with a short straddle.(1/n)

You can also view the position as a combination of Cal & Put credit spreads, if that makes it more easy for you.

There are 3 important things to understand while trading this strategy:

1) Initial size of the Wings
2) Risk Management
3) Adjustments

(2/n)

Since we are selling an ATM straddle, the 1st question is how far our wings should be? Ideally i sell .50 delta straddle & buy .20 or .10 OTM strangle, depending on my view on volatility. So the distance of wings depends on the IV setup. Higher the IVs, greater the distance.(3/n)

If you don't understand greeks, then ideally with 30 days to expiry (dte), wings should be around 300pts either side. If your trading in weekly then it should be not more than 200pts. Higher the premiums, higher the distance as we have more cushion of theta. (4/n)

It is important to understand that we need to reduce the distance of wings with time so as to manage our RISK in gap openings or sudden volatile move. So for eg. if you started with 300pt wings with 30dte, the wings wouldn't give the same protection when there is 7dte. (5/n)

Nonlawyer Explainer Thread: On Keeping One's Mouth Shut

It occurs to me that certain private-jet-flying seditionists who continue to yammer on Twitter about their DC excursions provide us with the opportunity to do a little hypo to explore the benefits of silence.

So let's explore what a hypothetical law enforcement interview *might* look like in this situation. I'm not - I want to make clear - drawing from experience as a lawyer here.

I AM NOT A CRIMINAL LAW ATTORNEY.

Instead, I'm mostly drawing from discussions with my father-in-law.

My father in law is a now-retired homicide cop, and we've had a lot of discussions (especially since I started law school) about criminals and interviews over the years.

So with that in mind, let's look at this hypo.

ALSO - Simplifying for Twitter character counts.

*Knock*
*Door opens*
Agent: Ms [Name]? I'm Agent Smith, and this is Agent Jones. We're with Agency. We'd like to talk to you if you've got a minute.

Ms X: Oh? Is this about that thing at the Capitol?

[Yes, it seems insane but if you're worried about something specific and the cops show up, blurting out something like that is totally a thing that can happen.]

It's a slow, snowy afternoon. How about a 🧵 on "rationalists" & "rationalism"? I want to talk about what real rationalism might look like & what people devoted to rationalism might actually behave like--and how that differs from what you often see from self-styled rationalists.

Caveat up front: this is not about Slate Star Codex, which I haven't read regularly enough to have an opinion on, or about the recent controversy between SSC & the NYT. I'm more interested in the *idea* of rationalism (vs. the practice).

The core premise of rationalism, as I understand it, is simply that humans' cognitive machinery was not designed by evolution to find truth, but rather to advance the interests & welfare of the collective -- a Venn overlap, but not the same thing. Therefore ...

... reasoning well, both individually & as groups, requires special effort. It requires consciously trying to set aside the parochialism, biases, & other distortions that typically characterize our thinking -- resisting, to some extent, the dynamics of group membership/welfare.

That's all fine. I agree entirely that we should make special effort to reason well & to guard against the typical failures of reasoning to which we humans are prone. I believe it's the best (maybe only) way forward as a species. So far so good.