我仔细研究了一下这个two_side,看它的语法: varlist has the dependent variables as its first element and the group-identifier as its last element. 代码的第一个变量是因变量,最够一个变量是分组的标识变量,面板数据应该一般就是时间。If the panel is unbalanced, the weight given to all the comparisons for unit i is 1/T(i). 如果所有的面板数据是非均衡的,就要按照这个方法赋权重。