The Core Question

From the previous post, the core question asked by the forensic analyst was:

How likely is the DNA profile we found if we assume the suspect committed the assault?

versus

How like is the DNA profile we found if we assume some unrelated person committed the assault?

How would we apply such thinking generally to non-forensic questions? Generalizing the core question looks like this:

How likely are the fact(s) I can truly verify if we assume one hypothesis?

versus

How likely are the fact(s) I can truly verify if I assume a competing hypothesis?

In the forensic case, the fact that can be verified and relied on is the resulting DNA profile. Everything else involved in the case the analyst was not around to witness and should be part of the "assumption" and not the facts.

In the general case, let's use a hypothetical model involving a contentious political issue. Let's say that the hypothetical state of Beatnikia bans all guns to alleviate their burgeoning gun crime problem. Some folks hate this law, claiming that it will disarm law-abiding citizens and cause crime to escalate. Other folks love this law, hoping that they'll finally be safe from gun-crazy criminals.

A federal study carefully monitors the results and finds that ten years after the ban was enacted that gun crime is roughly the same. What would be a clear-headed line of thinking? That gun crime would be lower if we hadn't disarmed the citizenry? That gun crime remained the same because gun nuts are hoarding their guns and selling them to criminals? Without further information, neither of these ideas are particularly clear-headed. These statements reek of confirmation bias, a beast discussed in an earlier posting.

the one fact we can verify is that gun crime rates are the same. Thinking forensically about that result might lead to the following questions:

How likely would that be if our law had any effect on gun crime vs. something else going on?

How likely would that be if one or the other group of concerned citizens were correct versus neither of them were correct?

How likely would that be if we really didn't understand the problem of gun crime?

This example sounds trite, but the core argument is profound. If we ask predictive questions only about the facts we can verify, we keep our heads even when things don't go our way. We no longer have to be "right" or "wrong", we merely transition from one honest idea to the next. Our theories, despite how dear they are to us, live and die on the facts we know are true.

It's a liberating idea. Imagine how much more interesting political debate would be if the participants first determined what facts they could rely on and weighed the probability of those facts given different sets of assumptions. It's a hopeless pipe dream to expect the talking heads who sell advertising for MSNBC and Fox News to embrace this idea, but most people aren't so completely compromised.

I'm not so naive as to expect some sea change in our political landscape. Politics will still be contentious and mean-spirited. Nonetheless, this "forensic" approach permitted thoughtful conversation and debate even when my fellow interlocutor disagreed with me completely. What's more, I almost always learned something from the discussion.