wp not found  就是加权变量wp没有被定义。
去掉[aw=wp]这个计算加权frequency的选项，除非特殊目的，一般不用。

aweights, or analytic weights, are weights that are inversely proportional to the variance of an observation; that is, the variance of the jth observation is assumed to be sigma^2/w_j, where w_j are the weights. Typically, the observations represent averages and the weights are the number of elements that gave rise to the average. For most Stata commands, the recorded scale of aweights is irrelevant; Stata internally rescales them to sum to N, the number of observations in your data, when it uses them.

请问这个加权变量一般是用来干什么的？我是新手，不太懂，谢谢

简单的说很多时候就是用来修正样本和总体之间的差别。比如总体有20男10女，但是样本只有1男1女，那么这个时候给样本里男性观测值两倍于女性观测值的权重，样本就能更符合总体。

好的，太棒啦！谢谢