Table 1 Model parameters
Parameter | Value | Evidence source and type |
|---|---|---|
Epidemiological | ||
Length of untreated episode of recurrent depression | 3rd episode: 0.55 years. | [32] 10 year observational study |
4th episode: 0.60 years | ||
5th episode +: 0.43 years | ||
Probability of no future recurrence of depression | 2 prior episodes: 0.3. | [33] |
3+ prior episodes: 0.1 | ||
Time to relapse | 0.93 years | [34] 15 year observational study |
Clinical presentation | ||
Probability of presenting to services during depressive episode | 0.40 | [35] Consensus document |
Probability of no relapse after cognitive behavioural therapy (CBT) response | 0.75 | [36] Randomised controlled trial |
Primary care | ||
Probability of medical therapy (even if stepping up) | Assumed 100% | Clinical expert assumption |
Probability of response after 8 weeks of mirtazapine anti-depressant therapy | 0.63 | |
Probability of IAPT referral | Assumed 100% | Clinical expert assumption |
IAPT | ||
Probability of low intensity IAPT | 0.68 | SHSC data |
Probability of high intensity IAPT | 0.32 | |
Probability of effective low intensity IAPT (> 10 point improvement in PHQ9) | 0.24 | |
Probability of effective high intensity IAPT (> 10 point improvement in PHQ9) | 0.54 | |
Probability of completing low intensity IAPT | 0.35 | |
Probability of completing high intensity IAPT | 0.35 | |
Number of low intensity IAPT sessions | 3 + 1 assessment | |
Number of high intensity IAPT sessions | 7 + 1 assessment | |
Length of course of low intensity IAPT | 0.42 years | |
Length of course of high intensity IAPT | 0.71 years | |
Community Mental Health Teams | ||
Time from referral to assessment | 0.08 years (4 weeks) | Clinical expert opinion |
Probability of accepted at assessment | 0.8 | |
Treatment effectiveness | CMHT treatment effectiveness assumed equal to IAPT | |
Specialist Psychotherapy Services | ||
Probability of being accepted at SPS assessment | 0.71 | SHSC data |
Treatment effectiveness | SPS treatment effectiveness assumed equal to IAPT | Clinical expert opinion |
Costs | ||
GP | £38 | 2009 NHS Unit Costs |
IAPT Therapist (per session) | £88 | 2010 NHS Reference Cost |
CMHT Assessment | £212 | |
CMHT Therapist (per session) | £135 | |
SPS Assessment | £139 | |
SPS Therapist (per session) | £139 | |
Mirtazapine treatment. 30 mg daily, 8 week course which if effective is maintained | £4.08 per course | BNF 61 |
Health Utilities | ||
Untreated severe depression | 0.30 | |
In health service, severe depression | 0.58 | |
Minimal depression/normal health | 0.85 | |