各位板上的大神

请问关于这个dea的题目该如何操作

   Using the data in cash_US_2000.data, create the following variables: na=ta_usd- cash; chna=cash/na; mtb=(ta_usd-ce+mc)/ta_usd; cfna=(ebit+da–interest –tax- dividend)/na; size=ln(ta_usd); dmu=_n. Obtain the efficiency scores based on varying returns to scale by using chna, cfna, leverage, and size as the inputs and mtb as the output. (Hint: size is the natural log of total assets in USD; cash means cash holdings; mtb is market-to-book ratio; cfna is a proxy of profitability; leverage is the ratio of debt to total assets; dmu is the decision making unit in DEA.)

(a)      Investigate whether and how the efficiency derived is influenced by chna and size. Are the results intuitive? Explain.

(b)     Consider incorporating a non-linear relationship between size and efficiency by including size-squared in the model. How are the results thus obtained compared to those in (a)?

我一开始跑 dea chna cfna leverage size = mtb , rts(vrs)

但是跑很久、结果也很长，我这样操作是否错误？

这题正确该如何执行、如何解释与回答题目呢？

附上资料档与新增变数的指令：

• g na=ta_usd- cash
• g chna=cash/na
• g mtb=(ta_usd-ce+mc)/ta_usd
• g cfna=(ebit+da-interest-tax-dividend)/na
• g size=ln(ta_usd)
• g dmu=_n