Williams A D
Demography. 1977 Nov;14(4):581-90.
Recent studies of the impact of child mortality on children ever born have used the "replacement factor" to measure mortality. When microlevel data are used, however, use of the replacement factor (or other variables which are nonlinear in the family's experienced child mortality rate) yields biased coefficients. An alternative model suggests a sequential, rather than a static, decision-making process to relate the decision to have an additional child to the reproductive experience to date. In this case, unbiased coefficients are obtained if the functional form is correctly specified. In the abscence of a priori knowledge of the functional form, it is difficult to untangle true effects from spurious ones.
近期关于儿童死亡率对曾生育子女的影响的研究使用了“替代因子”来衡量死亡率。然而，当使用微观层面的数据时，使用替代因子（或其他在家庭经历的儿童死亡率方面呈非线性的变量）会产生有偏差的系数。一种替代模型提出了一个顺序性而非静态的决策过程，将生育更多子女的决策与迄今为止的生育经历联系起来。在这种情况下，如果函数形式被正确设定，就能得到无偏差的系数。在缺乏函数形式的先验知识的情况下，很难从虚假影响中分辨出真实影响。
