## Table 1 |
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Model parameters |
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Parameter |
Value |
Evidence source and type |

Epidemiological |
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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 |
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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 |
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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 | [3,37] NICE Clinical Guideline |

Probability of IAPT referral | Assumed 100% | Clinical expert assumption |

IAPT |
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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 |
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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 |
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Probability of being accepted at SPS assessment | 0.71 | SHSC data |

Treatment effectiveness | SPS treatment effectiveness assumed equal to IAPT | Clinical expert opinion |

Costs |
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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 |
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Untreated severe depression | 0.30 | [3,38] NICE Clinical Guideline/Cohort analysis |

In health service, severe depression | 0.58 | |

Minimal depression/normal health | 0.85 |

Tosh * et al.*

Tosh * et al.* *BMC Health Services Research* 2013 **13**:150 doi:10.1186/1472-6963-13-150