EBM --- Journal Reading

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• EBM --- Journal Reading

Presenter??? Date2005/10/27
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Users Guides to the Medical Literature?. How
to Use a Clinical Decision AnalysisA. Are the
Results of the study Valid?
W. Scott Richardson, MD. Allan S. Detsky, MD,
PhD, for the Evidence-Based Medicine Working Group
JAMA April 26, 1995 273, 16
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What is Clinical Decision Analysis?

• ..the application of explicit quantitative
  methods to analyze decisions made under
  conditions of uncertainty.
• In more simple term..
• It uses a mathematical formula to reconstitute
  the whole scenario, helping clinicians to
  visualize choices that are available and make
  appropriate decisions.

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• Decision analysis helps clinicians to compare the
  expected consequences of pursuing different
  strategies.
• A decision analysis model must compare at least
  two decision options.
• The process involves identifying all the
  available management options, and the potential
  outcomes of each, in a series of decisions that
  have to be made about patient care.
• Each decision option can be more clearly
  evaluated, and a strategy can be identified for
  maximizing clinical utility and minimizing
  related health care costs.
• The range of choices are plotted on a decision
  tree.

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Analyzing the Analysis

• 1. Are The Results Valid?
• 2. What Are The Results?
• 3. Will The Results Help Me in Caring For My
  Patients?

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Are the Results Valid?

1. Were all important strategies and outcome
   included?
2. Was an explicit and sensible process used to
   identify, select, and combine the evidence into
   probabilities?
3. Were utilities obtained in an explicit and
   sensible way from credible sources?
4. Was the potential impact of any uncertainty in
   the evidence determined?

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1. Were all important strategies and outcome
included?

• The issue here is..
• how well the structure of the model fits the
  clinical decision analyses are built as decision
  trees
• Decision trees are displayed graphically,
  oriented from left-to-right.

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• Decision tree
• Illustrates all the potential choices and
  subsequent outcomes in
• diagrammatic form. The decisions and outcomes
  are presented in the order in which they are
  likely to occur, hence it is hierarchical in
  structure.
• Decision node
• A point in a decision tree where a decision has
  to be made. Generally illustrated by a square.
  The lines emanating from a decision node
  represent the clinical strategies being compared.
• Chance node
• Chance events that may occur following a
  decision. Generally illustrated by a circle. The
  probability of these events occurring are
  included in the decision tree
• Outcome node
• The final outcome of a decision path. Generally
  illustrated by a triangle or rectangle.

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2. Were all of the realistic clinical strategies
compared?

• Strategies ? sequences of actions and decisions
  that are contingent on each other
• The authors of the analysis should specify which
  decision strategies are being compared
• Clinical strategies should be described in detail
  to recognize them as separate and realistic
  choices.

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3. Were all clinically relevant outcomes
considered?

• To be useful to clinicians and patients, the
  decision model should include the outcomes of the
  disease that matter to patients.
• These include not only the quantity of life, but
  also the quality, in measures of disease and
  disability.

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• The specific disorder in question determines
  which outcomes are clinically relevant.
• E.g..
• For an analysis of an acute, life-threatening
  condition, life expectancy might be appropriate
  as the main outcome measure
• In an analysis of diagnostic strategies for a
  nonfatal disorder, more relevant outcomes would
  be discomfort from testing or days of disability
  avoided.

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• Clinical decision analyses should be built from
  the perspective of the patient, that is, should
  include all the clinical benefits and risks of
  importance to patients.
• By comparing the outcomes between strategies, you
  can discover the trade-offs (between competing
  benefits and competing risks) built into the
  model.
• The choice of strategies should be balanced on
  one or more of such trade-offs.
• The outcomes are measured as quality-adjusted
  life expectancy, a scale that combines
  information about both the quantity and quality
  of life.

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4. Was an explicit and sensible process used
to identify, select, and combine the evidence
into probabilities ?

• To assemble the large amount of information
  necessary for a decision analysis, the authors
  should search and select the literature in an
  explicit and unbiased way, and then appraise the
  validity, effect size, and homogeneity of the
  studies in a reproducible fashion.
• In other words, authors should perform as
  comprehensive a literature review as is required
  for a meta-analysis.

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• Once gathered, the information must be
  transformed into quantitative estimates of the
  likelihood of events, or probabilities.
• The scale of probability estimates ranges from 0
  (impossible) to 1.0 (absolute certain).
• Probabilities must be assigned to each branch
  emanating from a chance node, and for each chance
  node, the sum of probabilities must add to 1.0.

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5. Were the utilities obtained in an explicit
and sensible way from credible sources?

• Utilities represent quantitative measurements of
  the value to the decision maker of the various
  outcomes of the decision.
• Utility The preference or desirability of a
  particular outcome. A commonly used utility scale
  ranges from 0 (worst outcome, usually death) to
  1.0 (excellent health)
• In a decision analysis built for an individual
  patient, the most credible ratings are those
  measured directly from that patient.
• For analysis built to inform clinical policy,
  credible ratings could come from three sources
• (1) direct measurements from a large groups of
  patients with the disorder in question and to
  whom results of the decision analysis could be
  applied
• (2) from published studies of quality-of-life
  ratings by patients
• (3) from an equally large group of people
  representing the general public

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6. Was the potential impact of any uncertainty
in the evidence determined?

• Much of the uncertainty in clinical decision
  making arises from the lack of valid literature.
• Even when it is present, published evidence is
  often imprecise, with wide confidence intervals
  around estimates for important variables.

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• Decision analyst uses sensitivity analysis to
  see what effect varying estimates for risks,
  benefits, and values have on the expected
  clinical outcomes, and therefore on the choice of
  clinical strategies.
• Estimates can be varied one at a time
• ? one-way sensitivity analyses
• two or three at a time
• ? multi-way sensitivity analyses