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 [3,37] NICE Clinical Guideline
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 [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

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