Today this shows up in my inbox:
weird but important question
these two guys have the same last name. they are both important to me and awesome for different reasons. what do you think are the chances that they are related? (brothers or first cousins?)
Interesting. Sounds to me like a risk intelligence question. Risk intelligence is “the ability to estimate probabilities accurately, it’s about having the right amount of certainty to make educated guesses.” As Donald Rumsfeld put it,
There are known knowns; there are things we know we know.
We also know there are known unknowns; that is to say, we know there are some things we do not know.
But there are also unknown unknowns – the ones we don’t know we don’t know.
Rumsfeld’s tortured syntax serves the point, because this stuff is hard to think about. It requires stepping outside of yourself to ask not how much you know, but how much you know about how much you know.
Back to the question at hand, but let’s try to put it in a more generic form. Two men have the same last name. They are both prominent, but for different reasons. They look alike, but not stunningly so. What is the chance they are related?
I’m putting the question in this more generic form to try to gain distance from it and gain an appreciation for the underlying probabilities. I suspect most people would try to answer the original email by staring at the two pictures until they come up with a number. This will almost certainly lead to what Daniel Kahneman calls substitution: substituting an easier problem for a more difficult one. In this case, substituting the question of how alike the two men look for the question of how likely they are to be related. Perhaps after pondering the pictures for a minute, someone might say 80% — but what he really means is they look 80% alike (whatever that means).
Clearly, their similarity in appearance is related to the question of how likely they are to be related, but isn’t the only factor. People who look more alike are more likely to be related, but many people who look alike are not related; and some people who are related do not look alike.
My first thought when I saw the pictures was, they have to be related. But on further reflection, I rate the chance to be rather low; certainly well below 50%. There are many people with some level of notoriety who look kind of similar and share a last name; most of them aren’t related. But it’s still very difficult to put an exact number on it. 15%?
What do you think?