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Tools for Decision Making Sections
Author Bio
Introduction
Part I
Expected Value Decision Making
Case Study 2: Patient History
Using a Decision Tree
Assigning Utility
Currently selected section: Expected Value and QALYs
Sensitivity Analysis
Conclusions: Case Study 2
Part III

References


Chapter 14: Tools for Decision Making: Expected Values and QALYs
        

Problem 2.5.1: Calculating QALYs

Now, see if you can calculate the QALYs for the "Treat Infection" option.
Use the assumptions and instructions that follow (see diagram below).

Assumptions ("Treat Infection"):

  • UloseLeg is 0.6.
Figure 2.5.2: Calculating QALYs for the "Treat Infection" Option
Decision tree for Treat infection. Calculating QALYs where UloseLeg is 10 x .6 and cure infection is 1.0, details in text.


Question 2.5.1: STEP 1

To calculate the expected value of the right hand node, you first "average out" (multiply the QALYs for one outcome by the probability of that outcome and sum over all the branches at the chance node) and then "fold back" (moving from right to left, multiply the probability of an event by the QALYs of the event).

Based on your calculation, select the correct formula to fill in the box labeled STEP 1 in the diagram below:

Figure 2.5.2a: Calculating QALYs for the "Treat Infection" Option
Decision tree for Treat infection. Calculating QALYs where UloseLeg is 10 x .6 and cure infection is 1.0. Problem requires conducting Step 1 at right hand node (lose leg or death).

 

Selection A [10 x 0.6] + [0] + [10 x 1.0] = 10.6
Selection B[10 x 0.6] x 0.125 = 0.075
Selection C[0.875 x 6] + [0.125 x 1] = 5.375
Selection D [0.875 x 6] + [0.125 x 0] = 5.25

 

Question 2.5.2: STEP 2

STEP 2: Calculate the QALYs at the left hand node, multiplying the QALYs at the right hand node by the probability of curing the infection. The QALYs for the "Treat Infection" option are 8.11 life years (see below).

Based on your calculation, select the correct formula to fill in the box labeled STEP 2 in the diagram below

Figure 2.5.2c: Calculating QALYs for the "Treat Infection" Option
Decision tree for Treat infection. Calculating QALYs where UloseLeg is 10 x .6 and cure infection is 1.0. Problem requires conducting Step 2 at left hand node (treatment fails or save foot). Step 1: [0.875 x 6] + 0.125 x 0] = 5.25.

 

Selection A [0.4 x 5.25] + [0.6 x 10] = 8.11
Selection B [0.6 x 10] + [0.4 x 6] = 8.4
Selection C[0.125 x 0] + [0.875 x 10] = 8.75
Selection D[0.6 x 5.25] + [0.6 x 10] = 9.15

 

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