Primary Results: Progressive Disease
| Strategy | ICER |
|---|---|
| Status Quo | - |
| Treatment | 49,513 |
| Prevention | 139,630 |
Treatment is cost-effective at WTP=$50,000/QALY—but barely.
How sensitive is this result to the input parameter values used?
Deterministic, Threshold and Scenario Analyses
Learning Objectives and Outline
Learning Objectives
Explain the purpose of deterministic sensitivity analysis and provide examples of one-way versus two-way analyses.
Detail the advantages/disadvantages of deterministic sensitivity analysis.
Outline
- Net Benefit Outcome Measures
- One-way sensitivity analysis.
- Two-way sensitivity analysis.
- Limitations and extensions.
- Threshold analysis
- Scenario analysis
Alternatives to ICERs
- ICERs the most common approach for describing CEA results
- Good: summarize all aspects of decision problem except WTP (which comes from decision-maker)
- Bad: algorithms a bit complicated, negative ICERs, ratios can act poorly when denominator uncertain
An Alternative
- If willing to choose a fixed willingness-to-pay threshold (e.g., \lambda = 100,000 / QALY), can write down an equation for the contribution of health and cost to utility.
- Net Health Benefit (NHB)
- Net Monetary Benefit (NMB)
- Objective: Select the strategy with the highest NHB/NMB
Net Health Benefit (NHB)
\text{NHB}_s = E_s - \frac{C_s}{\lambda} where E_s is effectiveness of strategy s, C_s is cost of s and \lambda is WTP threshold.
Net Health Benefit (NHB)
\text{NMB}_s = E_s \times \lambda - C_s where E_s is effectiveness of strategy s, C_s is cost of s and \lambda is WTP threshold.
Example: NHB
E_1 = 0.07 years
E_2 = 0.10 years
C_1 = 1,500
C_2 = 2,800
\lambda = 50,000 per year of life saved
ICER = \frac{2800-1500}{0.10 - 0.07} \\ = 43,333 \\
Example: NHB
NHB_1 = 0.07 - 1500/50000 = 0.040 \\ NHB_2 = 0.10 - 2800/50000 = 0.044 \\ \text{Incremental } NHB = 0.044 - 0.040 = 0.004
Example: Net Monetary Benefit (NMB)
NHB_1 = 0.07 \times 50000 - 1500 = 2000 \\ NHB_2 = 0.10 \times 50000 - 2800 = 2200 \\ \text{Incremental } NHB = 2200 - 2000 = 200
Calculating NMB in Amua
Sensitivity
- ICER for Prevention strategy is just above WTP threshold of $50,000/QALY.
- NMB for treatment only slightly above NMB for prevention.
- How sensitive are these results to changes in specific model inputs?
One-way sensitivity analysis
One-way sensitivity analysis
- Usually the starting point for sensitivity analyses
- Sequentially testing one variable at a time (i.e., Age, BMI, QALY, other clinically important parameters), while holding everything else constant
- Determining how this variation impacts the results
- One-way sensitivity analyses are often presented in a tornado diagram
- Used to visually rank the different variables in order of their overall influence on the magnitude of the model outputs
Examples from publications
Rotavirus study
Rotavirus study
Rotavirus study
Other examples
Other examples
Other examples
Other examples
Interactive Amua Session
Two-way sensitivity analysis
Two-way sensitivity analysis
- A way to map the interaction effects between two parameters in a decision analysis model
- Varies 2 parameters at a time
- Explores the robustness of results in more depth
Examples from publications
HIV prevention
HIV prevention
Markov model examining strategies for HIV prevention among serodiscordant couples seeking conception (woman does not have HIV and male has HIV)
We know that if the male partner is consistently on medication for HIV (i.e., resulting in virologic suppression), then the risk of transmission is small regardless of the woman taking PrEP (pre-exposure prophylaxis)
And we also know that PrEP has traditionally been really costly
HIV prevention
Financial incentives for acute stroke care
Financial incentives for acute stroke care
Under pay for performance policies in the US, physicians or hospitals are paid more for meeting evidence-based quality targets
Study objective: Illustrate how pay-for-performance incentives can be quantitatively bounded using cost-effectiveness modeling, through the application of reimbursement to hospitals for faster time-to-tPA for acute ischemic stroke
Financial incentives for acute stroke care
When administered quickly after stroke onset (within three hours, as approved by the FDA), tPA helps to restore blood flow to brain regions affected by a stroke, thereby limiting the risk of damage and functional impairment
Financial incentives for acute stroke care
Interactive Amua Session
Limitations of deterministic sensitivity analyses
Caution: Limitations!
- Limited by the subjectivity of the choice of parameters to analyze
- That’s why we also run PSAs!, i.e., varying ALL input parameters at the same time, using priors to play a distribution around each value
Scenario analysis
Motivation
- Suppose we wanted to model the impact of these interventions under a “lower cost” scenario.
- One option is to
- It may be more efficient to define different scenarios rather than add additional strategies to the model structure itself.
Scenario analysis
- Focuses more on model assumptions rather than parameter uncertainty
- Could include separate analysis on:
Subgroups/sub-populations, including different age cohorts & risk levels
Different perspectives (societal; modified societal; etc)
Scenario analysis
Hypothetical scenarios (“optimistic” and “conservative” scenarios; for example, if we have little evidence of long-term survival associated with medication X, we might have an optimistic versus conservative scenario)
Time horizons
Examples
Examples
Examples
Examples
Examples
Examples
Threshold analysis
Threshold analysis
- Answers the question: What the input parameter need be to meet the country thresholds of:
- $50,000/QALY gained
- $100,000/QALY gained
- $150,000/QALY gained
- $200,000/QALY gained
Examples
Examples
