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在定群研究中,一般要计算发病密度。发病密度的分母用人-时数(人-年数或人-月数等等)。但无确切的公式应用。这往往给研习和记忆(特别是初学者及上机运算)带来不便。笔者在学习研究过程中,总结出大样本资料观察人-年数的计算公式及其简化式。现阐释如下,供参考。设,有一供定群研究观察的时间人群数列,如下表(表1)。表1 定群研究观察资料各年末存活人数按定义,暴露人-年数的计算方法如式1。即L=(X_1+X_2)/2+(X_2+X_3)/2+(X_3+X_4)/2 +…+(X_(n-2)+X_(n-1))/2+(X_(n-1)+X_n)/2 (式1)式中(X_1+X_2)/2为n=2 那一年的暴露人- 年数,余类推。将式进一步推导,得
In the study of population, the density of disease is usually calculated. Density denominator of the population - hours (people - years or people - months, etc.). But there is no exact formula to apply. This tends to inconvenience learning and memory (especially for beginners and computer operations). In the process of study and study, the author summarizes the calculation formula and simplification of observer - year for large sample data. Now explain as follows, for reference. Suppose there is a time series of population for observing the population, as shown in the following table (Table 1). Table 1 population research observation data by the end of the number of survivors by definition, exposures - years calculated as formula 1. That is, L = (X_1 + X_2) / 2 + (X_2 + X_3) / 2 + (X_3 + X_4) / 2 + ... + (X_ (n- 2) + X_ (n- 1)) / 2+ n-1) + X_n) / 2 (Eq. 1) where (X_1 + X_2) / 2 is the year of exposure in year n = 2, and so on. To further derive, too