Table 9:
Sensitivity Analysis: Description of Structural and Parameter Assumptions in Probabilistic Sensitivity Analysis Scenarios
| Parameter/Assumption | Base Case Analysis | Scenario Analysis: Major Changes in Parameter Values or Assumptions |
|---|---|---|
| 1. Population | MDD and GAD | GAD only: efficacy of CBT and number of CBT sessions (n = 10) |
| 2. Initial disease severity | Patients with both mild and moderate to severe MDD | Patients with mild MDD only; patients with moderate to severe MDD only |
| 3. Efficacy of interpersonal therapy | RR for CBT: 0.68 (0.53–0.76) | RR for interpersonal therapy: 0.41 (0.27–0.63) |
| 4. Efficacy of CBT | See Table 5 | Reduction of efficacy by 25% |
| 5. Dropout | See Table 4, different among treatment options | 2 × base case probability; 0.5 × base case probability |
| 6. Probability of not being well after dropout | 0.33 | 2 × base case probability; 0.5 × base case probability |
| 7. Rate of recurrence | Table 5, Eaton 2008,100 10-year survival curves | Table 5, NEMESIS,99 20-year survival curves |
| 8. Rate of hospitalization | 0.10 | 2 × base case rate; 0.5 × base case rate |
| 9. Additional disutility owing to past MDD | Yes | No |
| 10. Utility of CBT treatment 10% lower | 0.85 | 0.77 |
| 11. Number of CBT sessions | 14 | Analysis 1: 6 Analysis 2: 20 |
| 12. Costs of physician-provided CBT | Conservative assumption: psychiatrist (data shown in Table 7) | GP (data shown in Table 7) |
| 13. Costs of nonphysician-provided CBT, salary-based FTE: 1,658 hours/year | Conservative assumption: salary of $130,000/year + 30% benefits (see Table 7) | 1: $130,000/year + 17% benefits 2: $110,000/year + 30% benefits 3: $110,000/year + 17% benefits |
| 14. Costs of CBT, 2 providers | Psychiatrist or highest applied salary for nonphysicians ($130,000/year + 30% benefits) | GP or lowest applied salary for nonphysicians ($110,000/year + 17% benefits) |
| 15. Direct medical costs | All costs | CBT-associated costs: assessment, CBT treatment, 1-year follow-up |
| 16. Costs of complex depression | Responders | Nonresponders |
| 17. Follow-up costs | Costs associated with biweekly visits for first 4 months, then monthly visits | Decrease in frequency of follow-up (owing to lack of compliance) by 25%, 50%, and 75% |
| 18. Discount rate | 1.5% | 5% |
| 19. Time horizon | 5 years | 1: 1 year 2: 2 years 3: 10 years 4: 20 years 5: Lifetime |
Abbreviations: CBT, cognitive behavioural therapy; FTE, full-time equivalent; GAD, generalized anxiety disorder; GP, general practitioner; MDD, major depressive disorder; RR, relative risk.