大家好，我是一个自学stata的人，前几天刚买了那个state精品课，目前在自学。
最近研究一篇 关于二手车价格异常的文献，找到了它的stata指令，有一个地方看不懂，想请教下论坛里的大拿。
如下：
**Real values | No controls
reg price totalage totalage2 totalage3 totalage4 totalage5 older* if totalage<=108, robust
totalage是汽车年龄，后面的那个2-5分别是2次方，3次方，4次方，5次方，不明白作者这样做的计量意义。

------------------如下是其它的几个指令，假如有大神略得闲赋，望不吝赐教。

**Real values | With controls, No Model FE, No ModelUpdate controls （下面的指令是随机效应？mileage displacement horsepower fuel transmission extras是控制变量，也就是汽车特征）
reg price totalage totalage2 totalage3 totalage4 totalage5 older* mileage displacement horsepower fuel transmission extras* private if totalage<=108, robust

**Real values | With controls, No Model FE, ModelUpdate controls （这个是固定效应？modelupdatedummy是虚拟变量）
reg price totalage totalage2 totalage3 totalage4 totalage5 older* mileage displacement horsepower fuel transmission extras* private modelupdatedummy if totalage<=108, robust

**Real values | With controls, Model FE, No ModelUpdate controls
reg price totalage totalage2 totalage3 totalage4 totalage5 older* mileage displacement horsepower fuel transmission extras* private fe_audia4 fe_bmw3 fe_mercedesa fe_vwgolf if totalage<=108, robust

**Real values | With controls, Model FE, ModelUpdate controls
reg price totalage totalage2 totalage3 totalage4 totalage5 older* mileage displacement horsepower fuel transmission extras* private fe_audia4 fe_bmw3 fe_mercedesa fe_vwgolf modelupdatedummy if totalage<=108, robust

**Real values | With controls, Model FE, ModelUpdate controls | Commercial sellers
reg price totalage totalage2 totalage3 totalage4 totalage5 older* mileage displacement horsepower fuel transmission extras* fe_audia4 fe_bmw3 fe_mercedesa fe_vwgolf modelupdatedummy if totalage<=108 & private==0, robust

**Real values | With controls, Model FE, ModelUpdate controls | Private sellers
reg price totalage totalage2 totalage3 totalage4 totalage5 older* mileage displacement horsepower fuel transmission extras* fe_audia4 fe_bmw3 fe_mercedesa fe_vwgolf modelupdatedummy if totalage<=108 & private==1, robust