看陈强老师的高级计量经济学及stata运用clogit回归的相关部分时，书上只说了怎么进行回归，没说怎么检验IIA，help IIA之后：

IIA的语句为：
iia depvar varlist [if exp] [in exp] [weight], group(varname)
            code(varname) [ clogit-options ]

相关描述为：
Estimates McFadden's discrete choice model (with clogit) and subsequently
performs Hausman tests for the assumption of "independence of irrelevant
alternatives" (IIA) for each of the alternatives.

即，从相关描述来看，这个IIA命令可以进行clogit回归，并在回归之后进行IIA检验

例子为：
We have data on choices of means of transportation by a number of subjects. For
each subject and for each of his feasible alternatives (e.g., car, public
transportation, bike/walk) our data comprises measures of the monetary costs
(money), the time costs (time), and the "comfort costs" (comfort). clogit and
hence iia requires a data organization in which each (subject,alternative)
combination is described in a seperate record. In your data you have to have
variables that identify subjects (say respnr) and alternative (say means). Then

    . iia choice money time comfort, group(respnr) code(means)

然后，我照猫画虎，输入：
iia  choice train bus time invc,group(id) code(mode)
出现提示：
Hausman's test for assumption of "Independence of Irrelevant Alternatives"

Category   #obs    Hausman    df      p
-----------------------------------------
option nodisplay not allowed


所以是哪里出问题呢？option nodisplay not allowed是不是说 IIA命令中的[ clogit-options ]必须要有？那么这个 [ clogit-options ]又是指什么呢？