OBJECTIVE: To evaluate application of variables from an observational study data set to calculate and compare workplace absenteeism and productivity costs using human capital approach (HCA) and friction cost approach (FCA). METHODS: This was a supplemental analysis to a completed prospective, six month observational migraine outcomes study within a managed care organization (MCO). Data collection included pharmacy claims, patient occupation, and patient self-reported workplace absenteeism, and productivity at baseline, 3 months and 6 months post sumatriptan treatment. Patients were included in this supplemental analysis if they completed all 3 self-reported surveys and used sumatriptan according to the MCO prior authorization program. The HCA was calculated as [(number days missed due to migraine)+(days worked with migraine symptoms)(100%-% effectiveness while working with migraine ymptoms)/100%]x(daily wage). The FCA was calculated as (average number of migraines per month)(average number of lost work days due to migraine)(work hours/day)(dollars of production/employee). RESULTS: There were 160 patients who met the inclusion criteria for this analysis. The total indirect costs using the HCA and FCA methodologies were $97,024 and $124,260 respectively. CONCLUSION: The methodology assumptions and estimates employed to value lost productivity in this migraine population significantly impacts the results obtained. Prospective data collection may be required to minimize assumptions and accurately capture variables needed to calculate and understand each indirect cost method. Further evaluation of the post hoc analysis of observational data sets to evaluate productivity costs is warranted.