Seasonality of hip fractures and estimates of season-attributable effects: A multivariate ARIMA analysis of population-based data

Introduction: This study examined seasonal variations in hip fracture rates using nation-wide, population-based data from Taiwan, a subtropical island with fairly uniform weather conditions (mean ambient temperature difference of 11.3°C between peak summer and peak winter months). Methods: All inpatients aged 45+ years included in the National Health Insurance Database between 1997 and 2003 and bearing an ICD diagnosis code 820 (fracture neck of femur) were included (n=102,792 cases). Results: Auto-regressive integrated moving average (ARIMA) modeling showed significant seasonality and an association of monthly hip fracture admission rates with ambient temperature among both sexes and all three age groups, 45-64, 65-74, and 75+ years. Crude rates show a significant trough during May-August (late spring and summer), followed by a sharp increase in September, and a discernible peak during November-February (late autumn and winter). Adjusted for seasonality, trend, and month, hip fracture rates are significantly reduced among males (b= -0.280, p