It is very important to calculate the frequency of diseases in disease monitoring and investigating its cause. In particular, in order to determine the incidence rate according to time, the incidence density (hereinafter referred to as incidence rate)...
It is very important to calculate the frequency of diseases in disease monitoring and investigating its cause. In particular, in order to determine the incidence rate according to time, the incidence density (hereinafter referred to as incidence rate) is used, which is calculated with the number of events divided by the total observation time. The indices for an incidence rate are clearly defined, but every researcher may use a different missing value processing range in the longitudinal data depending on how many follow-up failures occurred. Thus the number of events (especially, disease occurrence) may vary. In this regard, in this study we calculated the incidence rate in a number of ways using the actual longitudinal data by comparing and discussing the resulting differences.
The data used in this study were community-based cohort (Ansan and Anseong) and Korea Health Panel data. The community-based cohort (Ansan and Anseong) is a prospective cohort data based on the follow-ups conducted at a 2-year interval from 2001 to 2012. The Korea Health Panel data was based on follow-ups conducted every year from 2008 to 2012.
Incidence rates were reviewed by separating the numerator and denominator in the calculation formula. The numerator was defined as three ways (A, B, C) with regard to diabetes and hypertension, and the denominator was defined as three estimation methods (①, ②, ③) for the observation time to calculate the incidence rate.
When calculating and comparing the incidence rate in various ways, the incidence rates were found to differ depending on how to the events were defined differently. In addition, the differences in the observation time differed according to how long the failed follow up period was prior to the defined event.
Incidence rates may vary depending on how the event definition and the observation time, but in this study, we calculated the incidence rate in nine ways (numerator: 3 kinds, denominator 3 kinds) using two kinds of longitudinal data and compared the incidence rates. The causes of differences in the incidence rate were explained in detail. Therefore, for a study that aimed to investigate the incidence rates, it was suggested to describe clearly and in detail on the data processing and to record the version of concerned data to ensure that the same results can be obtained at reproduction. In addition, the results of this study are to be provided as the basic data for investigating the causes that may have effect on diseases, to be utilized for the prevention and early treatment of diseases and to be utilized for basic data for health policy development.