输入： xtreg 发展和享受类消费 总指数 年龄 年龄的平方 婚姻 健康状况 学历 性别 ln总收入 家庭规模 ln人均gdp i.hhid,fe
报错如下：
maxvar too small
    You have attempted to use an interaction with too many levels or attempted to fit a model with too many variables.  You need to
    increase maxvar; it is currently 5000.  Use set maxvar; see help maxvar.

    If you are using factor variables and included an interaction that has lots of missing cells, try set emptycells drop to reduce the
    required matrix size; see help set emptycells.

    If you are using factor variables, you might have accidentally treated a continuous variable as a categorical, resulting in lots of
    categories.  Use the c. operator on such variables.
r(907);