Bridging demography, epidemiology, and statistics: Acceleration in disease rates with age- The SIMPLE Method

Selection of appropriate summary measures that accurately and precisely capture not only disease burden, but also population structure and dynamics that contribute to disease patterns is challenging. Some of the common measures of disease burden in the elderly, such as age-adjusted rates and age-categorization of rates, while useful, can mask important population processes that contribute to such disease patterns, especially in the elderly. We used Medicare hospitalization data (1991-2004) and US Census Bureau counts to estimate age-specific, influenza-related hospitalization incidence in the elderly by influenza season on the state and regional levels. We observed that incidence increases exponentially with age, and therefore proposed a technique, the Slope Intercept Modeling for Population Linear Estimation (SIMPLE) method, that represented that trend by two parameters. There parameters consist of an intercept, which represents expected influenza incidence at age 65, and a slope, which represents the degree of exponential increase of influenza-related incidence by age for the elderly. R-squared values for these models ranged from 0.802 to 0.989 for states and between 0.935 and 0.995 for regions. These results suggest spatiotemporal trends in influenza-related cases in the elderly can be estimated accurately and precisely using the SIMPLE method. This method produces two meaningful and relevant measures that can be used as summary measures of disease in a population and reflect the underlying demographics and epidemiology of disease, and can be applied to other diseases that exhibit similar age patterns in the elderly population.