ABSTRACT
The purpose of this paper was to introduce the independence test and the SAS implementation for the "unstratified person-time data" and the "stratified person-time data". In "person-time data"， the sample size in each level of the treatment factor was expressed as "person-years". Furthermore， it was necessary to use the "incidence density" to replace the "incidence rate" in the usual qualitative data analysis. The paper introduced the concrete approaches of comparing the "incidence density" of the "unstratified person-time data" and the "stratified person-time data" in detail， and demonstrated the whole process of using SAS software to realize the calculation through two examples， including the SAS program code， the SAS output results， the results explanation and the conclusion statement.