A micro costing analysis of the development of a primary care intervention to improve the uptake of diabetic retinopathy screening

BACKGROUND: The application of economic analysis within implementation science is still developing and the cost of intervention development, which differs markedly from the costs of initial implementation and maintenance, is often overlooked. Our aim was to retrospectively cost the development of a multifaceted intervention in primary care to improve attendance at diabetic retinopathy screening. METHODS: A retrospective micro costing of developing the intervention from the research funder perspective was conducted. It was based on a systematic intervention development process involving analysis of existing audit data and interviews with patients and healthcare professionals (HCPs), conducting consensus meetings with patients and HCPs, and using these data together with a rapid review of the effectiveness of interventions, to inform the final intervention. Both direct (non-personnel, e.g. travel, stationary, room hire) and indirect (personnel) costs were included. Data sources included researcher time logs, payroll data, salary scales, an online financial management system, invoices and purchase orders. Personnel involved in the intervention development were consulted to determine the activities they conducted and the duration of their involvement. Sensitivity and scenario analyses were conducted to estimate uncertainty around parameters and scope. RESULTS: The total cost of intervention development (July 2014–January 2019) was €40,485 of which 78% were indirect (personnel) costs (€31,451). In total, personnel contributed 1368 h to intervention development. Highest cost activities were the patient interviews, and consensus process, contributing 23% and 34% of the total cost. Varying estimated time spent on intervention development activities by + 10% increased total intervention development cost by 6% to €42,982. CONCLUSIONS: Our results highlight that intervention development requires a significant amount of human capital input, combining research experience, patient and public experience, and expert knowledge in relevant fields. The time committed to intervention development is critical but has a significant opportunity cost. With limited resources for research on developing and implementing interventions, capturing intervention development costs and incorporating them as part of assessment of cost-effective interventions, could inform research priority and resource allocation decisions. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s13012-021-01085-4.