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Table 2 Methods for estimating unit costs

From: Retention in care, resource utilization, and costs for adults receiving antiretroviral therapy in Zambia: a retrospective cohort study

Resource Method
Fixed resources  
Buildings and equipment Estimated upfront investment costs using a replacement cost approach, then calculated annualized costs using a 3% annual discount rate and an estimated working life of 5 years for equipment and 50 years for buildings [11]. Annual building and equipment costs for the ART clinic at each site were divided by the total number of active HIV patients at the site per year to estimate a cost per patient-year in care. The total number of active HIV patients at the site was calculated by summing the number of ART patients at the site with the number of non-ART patient-equivalents weighted based on a ratio of the average number of patient visits to the site per year for non-ART versus ART patients.
Support staff Estimated annual cost of support staff employed in the ART clinic at the study sites during the study period based on 2011 salaries and allowances. The proportion of staff time allocated to ART versus non-ART activities was based on staff estimates. Annual support staff costs were divided by the total number of active HIV patients at the site per year to estimate a cost per patient-year in care. The total number of active HIV patients at the site was calculated by summing the number of ART patients at the site with the number of non-ART patient-equivalents weighted based on a ratio of the average number of patient visits to the site per year for non-ART versus ART patients. Costs for higher-level administrative support staff, including staff based in the health facility in which the ART clinic was located, were excluded from the analysis.
Variable resources  
ARV drugs Estimated as the average per unit cost for all units of a particular drug purchased for the Zambia national HIV program in 2011, or during the most recent year available if no units of a particular drug were purchased in 2011, as recorded in the Global Price Reporting Mechanism [12]. Data on ART regimen dispensed were used to determine the appropriate drug formulation (fixed dose tablet, single dose tablet) for each ARV drug dispensed [3].
Non-ARV drugs Estimated from standard Zambian Ministry of Health per package costs [13].
Laboratory tests For sites 3, 4, 5, and 6, where laboratory tests are run onsite, costs were estimated as the sum of unit costs for reagents, consumables, equipment, labor, and space. Costs of reagents and consumables were estimated from standard Zambian Ministry of Health per package costs [13]. Annual laboratory equipment, labor, and space costs were divided by the total number of laboratory tests performed per year to estimate a per test cost at each site. For sites 1 and 2, where laboratory tests are run at a centralized laboratory, costs were provided by the Centre for Infectious Disease Research in Zambia Central Laboratory in Lusaka and included the cost of reagents, consumables, equipment, and labor used for each test (Henry Latner, personal communication, April 29, 2011).
Provider time for clinic visits Estimated the total annual cost of staff time for each type of provider conducting patient consultations. The proportion of staff time allocated to ART versus non-ART activities was based on staff estimates. Cost per visit was calculated by dividing the total cost of staff time for each type of provider, valued at 2011 salaries and allowances, by the total number of patient consultations with each provider type per calendar year.