Socio‐economic inequality in health service utilisation: Does accounting for seasonality in health‐seeking behaviour matter?

Seasonal variation exists in disease incidence. The variation could occur across the different regions in a country. This paper argues that using national household data that are not adjusted for seasonal and regional variations in disease incidence may not be directly suitable for assessing socio‐economic inequality in annual outpatient service utilisation, including for cross‐country comparison. In fact, annual health service utilisation may be understated or overstated depending on the period of data collection. This may lead to miss‐estimation of socio‐economic inequality in health service utilisation depending, among other things, on how health service utilisation, across geographical areas, varies by socio‐economic status. Using a nationally representative dataset from South Africa, the paper applies a seasonality index that is constructed from the District Health Information System, an administrative dataset, to annualise public outpatient health service visits. Using the concentration index, socio‐economic inequality in health service visits, after accounting for seasonal variations, was compared with that when seasonal variations are ignored. It was found that, in some cases, socio‐economic inequality in outpatient health service visits depends on the socio‐economic distribution of the seasonality index. This may justify the need to account for seasonal and geographical variations.