Tuesday, May 5, 2009

Differential diagnosis, people!

House - "Haven't done the MUGA."
Wilson - "Then how do you know she needs a heart transplant?"
House - "Got my aura read today. Said someone close to me had a broken heart."
(Season 1)

Yes, I admit it, I'm an avid "House, MD" fan. The fun part about this show is that a lot of people find meaning that's beyond the plain action to relate to - much different, I assume, than what the writers meant. Some watch it for plain medical aspect, like a good mystery story; some treat House as their fictitious mentor; some like the twists of the tale. I sometimes watch it like a tale of business intelligence and a general case of decision making with partial information.

Here's how it usually goes: in comes a case. It either looks suspicious upfront or bad indicators come up immediately at the beginning (by the way, did you notice that in most of the first half of season 1, it was seizures?). Then they go through "Differential diagnosis" and run various tests; additional symptoms are discovered, and usually the truth is discovered by connecting details that hid from the doctors (because "everybody lies") or simply because they didn't connect the dots.

Yeah, real life medicine isn't that simple, and sometimes even knowing what happened is too complicated to be nailed down case by case. Obviously catharsis doesn't come, like clockwork, every 35 minutes - just in time for the drama. But it's pretty similar, isn't it? In comes buyer A, and presents the details of person B. Not much to say about buyer A - their IP connection (anonymized?), their email (opened yesterday?), purchase details, maybe shipping address. Nothing much on person B either - name, address, credit card number. Would you let the purchase go through? Differential diagnosis, people! What test can we run to verify this person, or establish fraudulent behavior? What does it mean if they can verify the email, answer a call to their mobile phone, tell you that the issuing bank is Citi? What additional indicators are we missing? Because that's what the "game" is - in comes a case - what do you do? No one is dying, but your balance sheet is going to look pretty bad.

The trick about decision making in this case is understanding what the next step is. Our goal, whether asking the customer for additional details or looking for an additional data source (what's next - Family history review? MRI? CT scan?), is to reach a conclusion in as little steps as possible, meaning that we need to be able to choose the steps that contain as much information as possible. BI experts sometimes tend to get as much data as possible, sometimes at enormous costs (these external vendors don't come cheap). House's department costs the hospital millions of dollars a year, but that's human lives. We need to be cost effective.

One major way to work with this is automated decision making systems - expert system - which help experts reach decisions by dealing with the quantity of data by using statistical models for classification. Advanced systems, when correctly fed with symptoms (or fraud indicators), can even suggest tests to rule out corner cases. Constructing such a system is the end station of the long road that starts with the single source of truth - in House's case, the doctor. In fact, expert systems in the field of medicine usually outscore doctors in identifying illnesses based on differential diagnosis - it only makes sense, when you hear House's staff shooting diagnoses based on remarkable memory and years of experience. Which brings out the question - why doesn't House use one? It would immensely scale his ability to save lives.

But then again, how much fun will that be?

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