The relationship between headache-attributed disability and lost productivity: 3 Attack frequency is the dominating variable.

backgroundIn an earlier paper, we examined the relationship between headache-attributed disability, measured as proportion of time in ictal state, and lost productivity. In a linear model, we found positive and significant associations with lost paid worktime, lost household worktime and total lost productivity (paid + household), but with high variance, which was increased when headache intensity was introduced as a factor. We speculated that analyses based on headache frequency alone as the independent variable, eliminating both the subjectivity of intensity estimates and the uncertainties of duration, might show stronger associations.

methodsFocusing on migraine, we used individual participant data from 16 countries surveyed either in population-based studies or in the Eurolight project. These data included frequency (headache days/month), usual attack duration (hours), usual headache intensity ("not bad", "quite bad", "very bad") and lost productivity from paid and household work according to enquiries using the Headache-Attributed Lost Time (HALT) questionnaire. We used multiple linear regressions, calculating regression equations along with unstandardized and standardized regression coefficients. We made line and bar charts to visualize relationships.

resultsBoth frequency and intensity were significant predictors of lost productivity in all multiple linear regressions, but duration was a non-significant predictor in several of the regressions. Predicted productivity in paid work decreased among males by 0.75-0.85 days/3 months for each increase of 1 headache day/month, and among females by 0.34-0.53 days/3 months. In household chores, decreases in productivity for each added day/month of headache were more similar (0.67-0.87 days/3 months among males, 0.83-0.89 days/3 months among females). Visualizations showed that the impact of duration varied little across the range of 2-24 h. The standardized regression coefficients demonstrated that frequency was a much better predictor of lost productivity than intensity or duration.

conclusionIn the relationship between migraine-attributed impairment (symptom burden) and lost productivity, frequency (migraine days/month) is the dominating variable - more important than headache intensity and far more important than episode duration. This has major implications for current practice in headache care and for health policy and health-resource investment. Preventative drugs, grossly underutilized in current practice, offer a high prospect of economic benefit (cost-saving), but new preventative drugs are needed with better efficacy and/or tolerability.