Models for Inexact Reasoning The Dempster-Shafer Theory of Evidence - - PowerPoint PPT Presentation

Models for Inexact Reasoning The Dempster-Shafer Theory

• f Evidence

(A Sample Scenario)

Miguel García Remesal Department of Artificial Intelligence mgremesal@fi.upm.es

Fed up with TV Series?

• A patient is admitted to the hospital with the

following symptoms:

• Dr. Houses’ team is taking the case
• Dr. Gregory House
• Dr. Eric Foreman
• Dr. Alison Cameron

After the Initial Physical Exploration

It’s viral.Most probably flu or just a regular cold. Gentlemen, place your bets! Yeah, I agree with

• Foreman. I’m

almost certain that it’s flu.

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viral_diseases cold, flu, ... cold, flu 0.8, 0.2 flu 0.9, 0.1

F F C C

m m m m Θ = = = Θ = = Θ =

A Bit Later…

Don’t worry. It’s just

• flu. You’ll be fine in a

week. Doctor, how long will it take to fully recover?

• Good. I gotta get back

to work ASAP. I’ve been on holidays in Canada last month. I cannot afford staying in bed for longer! I have to pay my bills! What do you do for a living? I’m a vet. I visit different farms to diagnose and treat the animals. cough, cough, cough…

Ummm… I don’t really like that dry cough… Besides, he’s been in rural zones, and has recently traveled to Canada… This makes Avian Influenza and SARS a moderately relevant hypothesis. However, I cannot discard either flu or a regular cold. To be sure, I will order a chest X-Ray.

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viral_diseases cold, flu, SARS, avian_influenza, ... cold, flu 0.3, SARS, avian_influenza 0.6, 0.1

H H H

m m m Θ = = = = Θ =

Just wait a minute…

New Symptoms

I find it difficult breathing!!! This makes SARS more probable. However, we will wait for the X-Rays.

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2 2

viral_diseases cold, flu, SARS, avian_influenza, ... SARS 0.7, cold, flu 0.3

H H

m m Θ = = = =

New evidence: the X-Rays

The results of the X-Rays: They show increased opacity in both

• lungs. This is a clear sign of pneumonia and respiratory distress
• syndrome. This hugely favours the SARS hypothesis.

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2 2

viral_diseases cold, flu, SARS, avian_influenza, ... SARS 0.99, cold, flu 0.01

C C

m m Θ = = = =

Diagnosis and Treatment

It’s obviously SARS. Give him antipyretics, supplemental oxygen and ventilatory support. Hopefully he will recover quickly. Yes, Sir