Our description of the study methods and results follows the consolidated health economic evaluation reporting standards (CHEERS) [29]. The data for this health economic investigation were gathered as part of the study “Intervention for children with parents with mental illness” CHIMPS [30].
Trial design
A multicenter randomized clinical trial (RCT) over an 18-month period was conducted at seven study sites in Germany (6) and Switzerland (1) to evaluate the effectiveness and cost-effectiveness of a family-focused intervention for children with parents having a mental illness [30]. Data were collected from all participating family members at baseline and at 6-, 12- and 18-month follow-ups. Families were recruited at in- and outpatient departments of psychiatric hospitals for adults and for children and adolescents. Families were eligible for study participation if they had at least one child between ages 3 and 19 and if at least one parent was treated because of mental illness during the last five years. Eligible families were randomly assigned to the intervention or control group after the baseline assessment had been completed. Further details of the trial design, recruitment and randomization procedures are published in the study protocol [30].
Intervention
Families in the intervention group received the intervention for children with a parent with mental illness (CHIMPs). CHIMPs is a manualized program [31] consisting on average of eight semi structured sessions (50 to 90 minutes) provided by a psychiatrist or psychotherapist over six months. Intervention providers were trained by the program developer. The program includes separate sessions with parents, each child and the entire family. The final number of sessions per family therefore depends on the number of participating family members. Further details of the CHIMPs intervention and the implementation of the program are provided in the study protocol [30].
Control condition
Families assigned to the control condition received no additional services beyond the routine treatment and care provided by the German health and social care system. Routine health care financed by mandatory or private health insurance includes medical in- and outpatient hospital treatment, ambulant treatment by office-based family doctors and specialized physicians including psychiatrists, ambulant psychotherapy, other ambulant therapies and medication. In addition to health care financed by health insurance, support for families with special needs is provided by child welfare services, which are tax-based and financed by communities [32]. For children and adolescents with particular educational needs, several types of school-based services, such as school social workers or school psychologists, are available, which are tax-based and financed by the communities or by the federal states [32].
Perspective and scope of the health economic evaluation
Due to the family-focused character of the intervention, health and psychosocial service use were assessed, and total costs were estimated for each participating family member. For the purpose of the health economic evaluation, we decided to perform separate analyses for children and parents, as we expected different results for both groups. This article reports only the results for children and adolescents.
An incremental cost-utility analysis taking the child or adolescent as the unit of analysis has been conducted from the perspective of the German health and social care welfare system. Therefore, only the data for children and adolescents from the six German study sites were included in this analysis. The analysis has a time frame of 24 months. For the incremental cost-utility analysis, we used an average 12-month time frame and two separate analyses for the first and second study years.
Discounting
Due to the short time frame, no discounting of costs and effects has been applied.
Measures
Costs
Total use of health care and psychosocial services of the children and adolescents was assessed by the Children and Adolescent Mental Health Service Use Inventory (CAMHSRI) [33] adapted for the German health and social care system [32]. Costs for service units used have been estimated on the basis of literature and internet search and by personal consultation of service providers, health insurances and other payers [32].
The intervention costs were estimated per child and per family. On average, each family received eight intervention sessions, one initiating session with parents and children (60 minutes), two sessions with both parents (60 minutes), one session with each child (50 minutes) and three group sessions for the entire family (90 minutes). The intervention could be provided by psychiatrists or psychologists. Therefore, costs for intervention staff were calculated as €102.57 per hour, representing the average hourly rate of a psychiatrist (€132.7) and a psychologist (€88.56). Given a total intervention time of 7 hours, total intervention costs amounted to €717.99 per family. Since each family had on average 1.6 children, costs per child were estimated at €450.
Outcomes
Outcomes of quality of life for children and adolescents were measured by means of the KIDSCREEN-10 [34]. KIDSCREEN data have been transformed into utility values by the algorithm provided by Chen et al. [35].
Statistical analyses
All statistical analyses were conducted on an intention-to-treat (ITT) basis. Missing values were imputed by the last observation carried forward (LOCF) method.
Average annual total costs were calculated by summing the six-month costs estimated at baseline and the three follow-up assessments divided by 2. Average annual QALYs were calculated as the area under the curve [36] by summing the 6-month utility values from baseline and the three follow-up assessments multiplied by 0.5 to obtain the average QALY over the two-year study duration, divided by 2 to obtain the average QALY. Separate annual costs and QALYs for the first and second years of the study were computed in an equivalent manner.
For the assessment of between-group differences in costs and effects, linear regression models were estimated for costs and outcomes, taking into account that the children were clustered within families by including family identification as a cluster variable. The skewed distribution of cost data has been taken into account by applying robust variance estimation [37].
Incremental cost-utility ratios (ICUR) were computed as annual averages over the total 24-month study period and separately for the first and second years of the study.
The ICUR variance and confidence intervals were estimated by means of nonparametric bootstrapping with 10.000 replications [36]. The probability of cost-effectiveness depending on willingness to pay (WTP) thresholds has been estimated by means of the cost-effectiveness acceptability curve, and the probability of obtaining a net monetary benefit has been estimated by means of the net-benefit regression curve [36].
All analyses were conducted with Stata 16.1 using the programs provided by Glick [36].