Medical Decision Making

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Medical Decision Making

• Although decision making is a prime activity of
  physicians, little time is spent on this subject
  in medical school curricula
• This lecture deals with the quantitative methods
  that can be used to aid physicians in decision
  making under uncertainty

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Questions for the Decision Maker

• Efficacy and Effectiveness of Dx Tech
• Evaluation of outcomes of care not process
• New sources of information, written, www, other
  high tech
• Rational limits to memory
• Understandability of probability concepts by Pat
  and Phy. Understand uncertainty

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Rationality Defined

• Based upon decision makers current assets
• Based upon possible consequences of choice
• When consequences uncertain, evaluated without
  violating basic rules of probability theory

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Representativeness Difficulties

• Prior probability not taken into account
• Insensitivity to sample size
• Misconstruing randomness
• Not taking disconfirmatory evidence into account
• Misconstruing regression to the mean

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Imagine you have the following scenario

• 1. If program A is adopted, 200 people will be
  saved
• 2. If program B is adopted, there is a 1/3
  probability that 600 people will be saved and a
  2/3 probability that no people will be saved

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Now compare the following

• 1. If program C is adopted, 400 people will die
• 2. If program D is adopted, there is a 1/3
  probability that no one will die and a 2/3
  probability that 600 people will die

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Availability

• When data are recent, familiar or salient they
  are more easily retrieved from memory and
  therefore seem more real than naturalistic
  frequencies

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Anchoring and Adjusting

• Original estimates of probability biased because
  of availability and representativeness heuristics
• When asked to adjust estimates based upon new
  information unlikely to apply correct amount

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Correct Use of Representativeness

• Evaluate how good are the cues
• Are they independent
• What is their prior probability
• Is the sample large enough
• Evaluate whether the results may be only
  regression to the mean

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Sample ProblemMrs. Hull

• 56 year old,white female,160,57 tall
• Smokes 1.5 pack cigarettes daily
• Increasing frequent episodes of typical angina,
  relieved by nitroglycerine
• Complete physical exam normal
• Special studies performed

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Mrs. Hull (cont1)

• Coronary angiography shows 2 vessel disease
• Question of therapy and outcomes
• Medical vs. surgical therapy

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Mrs. Hull (cont2)

• Perioperative mortality 2.5
• Three year mortality 4.8 after surgery and 7.2
  after medical therapy
• Probabilities of 3 levels of symptoms and death
  as outcomes

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Mrs. Hull Outcomes
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