最近看一篇外文，是这样说的：
To be consistent with the existing studies as well as due to the low power problem of unit-root tests, we chose to include the level of z in a VAR model.

说明一下：这是做三变量的SVAR模型，长期约束已经设置好了
问你是作者引入的这三个变量 x y z，前两个变量x和y都是对数差分后是平稳的，第三个变量z是取水平值，
作者给出的理由是
To be consistent with the existing studies as well as due to the low power problem of unit-root tests, we chose to include the level of z in a VAR model.

哪位高手请给出理解解释这段英文的意思？
当然不是翻译这段话

难道水平值的加入就能解决单位根检验的低效率？

是否有理论支持？
如果能解决，论坛币再送100