Discrete Event Simulation for Decision Modeling in Health Care: Lessons from Abdominal Aortic Aneurysm Screening

Markov models are often used to evaluate the cost-effectiveness of new healthcare interventions but they are sometimes not flexible enough to allow accurate modeling or investigation of alternative scenarios and policies. A Markov model previously demonstrated that a one-off invitation to screening for abdominal aortic aneurysm (AAA) for men aged 65 y in the UK and subsequent follow-up of identified AAAs was likely to be highly cost-effective at thresholds commonly adopted in the UK (£20,000 to £30,000 per quality adjusted life-year). However, new evidence has emerged and the decision problem has evolved to include exploration of the circumstances under which AAA screening may be cost-effective, which the Markov model is not easily able to address. A new model to handle this more complex decision problem was needed, and the case of AAA screening thus provides an illustration of the relative merits of Markov models and discrete event simulation (DES) models. An individual-level DES model was built using the R programming language to reflect possible events and pathways of individuals invited to screening v. those not invited. The model was validated against key events and cost-effectiveness, as observed in a large, randomized trial. Different screening protocol scenarios were investigated to demonstrate the flexibility of the DES. The case of AAA screening highlights the benefits of DES, particularly in the context of screening studies

Discrete Event Simulation for Decision Modelling in Health Care: Lessons from Abdominal Aortic Aneurysm Screening

Markov models are often used to evaluate the cost-effectiveness of new healthcare interventions, but they are sometimes not flexible enough to allow accurate modelling or investigation of alternative scenarios and policies. A Markov model previously demonstrated that a one-off invitation to screening for abdominal aortic aneurysm (AAA) for men aged 65 in the UK and subsequent follow-up of identified AAAs was likely to be highly cost-effective at thresholds commonly adopted in the UK (£20,000-£30,000 per quality adjusted life-year). However, new evidence has emerged and the decision problem has evolved to include the exploration of the circumstances under which AAA screening may be cost-effective, which the Markov model is not easily able to address. A new model to handle this more complex decision problem was needed and the case of AAA screening thus provides an illustration of the relative merits of Markov models and discrete event simulation (DES) models. An individual level DES model was built using the R programming language to reflect possible events and pathways of individuals invited to screening versus those not invited. The model was validated against key events and cost-effectiveness as observed in a large randomized trial. Different screening protocol scenarios were investigated to demonstrate the flexibility of the DES. The case of AAA screening highlights the benefits of DES, particularly in the context of screening studies

Should we screen women for abdominal aortic aneurysm? Analysis of clinical benefit, harms and cost-effectivenes

Backgroud: One-third of UK deaths from ruptured abdominal aortic aneurysm (AAA) are in women. In men, national screening programmes reduce deaths from AAA and are cost-effective. The benefits, harms and cost-effectiveness in offering a similar programme to women have not been formally assessed. Methods: A discrete event simulation model was set up for AAA screening, surveillance and intervention. Relevant women-specific parameters were obtained from sources including systematic literature reviews, national registry/administrative databases, major AAA surgery trials, and UK National Health Service reference costs. Findings: AAA screening for women, as currently offered to UK men (at age 65, AAA diagnosis at an aortic diameter of ≥3.0cm and elective repair considered at ≥5.5cm) gave, over a 30-yeartime horizon, an estimated incremental cost effectiveness ratio (ICER) of £30,000 (95% CI 12,000 to 87,000) per quality adjusted life-year (QALY) gained, with 3,900 invitations to screening required to prevent one AAA-death and an over-diagnosis rate of 33%. A modified option for women (screening at age 70, diagnosis at 2.5cm and repair at 5.0cm) was estimated to be more cost-effective, with an ICER of £23,000 (9,500 to 71,000) per QALY and 1,800 invitations to screening required to prevent one AAA-death, but an over-diagnosis rate of 55%. There was considerable uncertainty in the ICER, largely driven by uncertainty about AAA prevalence,the distribution of aortic sizes for women at different ages and the impact of screening on quality-of-life. Interpretation: By UK standards an AAA screening programme for women, mimicking that in men, is unlikely to be cost-effective. Further research on the aortic diameter distribution in women and potential quality of life decrements associated with screening are needed to assess the full benefits and harms of modified options

Should we screen women for abdominal aortic aneurysm? Analysis of clinical benefit, harms and cost-effectiveness

Background: One-third of UK deaths from ruptured abdominal aortic aneurysm (AAA) are in women. In men, national screening programmes reduce deaths from AAA and are cost-effective. The benefits, harms and cost-effectiveness in offering a similar programme to women have not been formally assessed. Methods: A discrete event simulation model was set up for AAA screening, surveillance and intervention. Relevant women-specific parameters were obtained from sources including systematic literature reviews, national registry/administrative databases, major AAA surgery trials, and UK National Health Service reference costs. Findings: AAA screening for women, as currently offered to UK men (at age 65, AAA diagnosis at an aortic diameter of ≥3.0cm and elective repair considered at ≥5.5cm) gave, over a 30-yeartime horizon, an estimated incremental cost effectiveness ratio (ICER) of £30,000 (95% CI 12,000 to 87,000) per quality adjusted life-year (QALY) gained, with 3,900 invitations to screening required to prevent one AAA-death and an over-diagnosis rate of 33%. A modified option for women (screening at age 70, diagnosis at 2.5cm and repair at 5.0cm) was estimated to be more cost-effective, with an ICER of £23,000 (9,500 to 71,000) per QALY and 1,800 invitations to screening required to prevent one AAA-death, but an over-diagnosis rate of 55%. There was considerable uncertainty in the ICER, largely driven by uncertainty about AAA prevalence, the distribution of aortic sizes for women at different ages and the impact of screening on quality-of-life. Interpretation: By UK standards an AAA screening programme for women, mimicking that in men, is unlikely to be cost-effective. Further research on the aortic diameter distribution in women and potential quality of life decrements associated with screening are needed to assess the full benefits and harms of modified options.The UK National Institute for Health Research (NIHR) Health Technology Assessment (HTA) programme commissioned this research (project number 14/179/01)