Problem Statement: Due to their perceived complexity, individual-based (patient level) models are often over-looked in health technology assessments (HTA) but can be valuable tools to deal with some of the inflexibility associated with cohort models. This case study describes the use of an individual-based approach to model the natural history and clinical pathway of patients with paediatric gliomas to inform decision-making.

Description: A decision analytic model was developed in Microsoft Excel using visual basic application to inform decision-making in paediatric patients with low and high-grade gliomas. During model conceptualisation, there were several aspects of the condition and treatment that needed to be considered, including (1) modelling two types of glioma that are associated with different prognoses and treatment pathways, (2) patients stopping treatment when reaching adulthood or according to an informal stopping rule, (3) the low/no risk of progression when patients reach adulthood, (4) treatment dosage that is dependent on age and weight and (5) modelling the progressive and worsening in quality of life in patients with high-grade gliomas toward the end of life. A cohort approach was initially attempted, but the implementation in Excel quickly became unmanageable and convoluted. Consequently, an individual based approach was eventually implemented using Visual Basic and allowed capture of the important aspects of the condition and treatment.

Lessons Learned: While some components were easier to implement in an individual-based approach, others were more challenging such as the inclusion of correlation and the sampling of the time to events. In this example, we believed that the use of an individual-based approach outweighed the downside. Following initial concern by external experts, providing a clear rationale and several validations were central for this approach to be accepted for HTA decision-making. Using a different platform such as R software could have helped with the implementation and transparency.

Stakeholder Perspective: Industry