. clogit choice01 area price year location environment time opportunity age education occupation worknumberper var14, gr
> oup(id) nolog
note: multiple positive outcomes within groups encountered.
note: age omitted because of no within-group variance.
note: education omitted because of no within-group variance.
note: occupation omitted because of no within-group variance.
note: worknumberper omitted because of no within-group variance.
note: var14 omitted because of no within-group variance.

Conditional (fixed-effects) logistic regression   Number of obs   =        783
                                                  LR chi2(7)      =      17.96
                                                  Prob > chi2     =     0.0122
Log likelihood = -376.50118                       Pseudo R2       =     0.0233

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    choice01 |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
        area |  -.1707955   .0753875    -2.27   0.023    -.3185523   -.0230387
       price |  -.0135165   .0767883    -0.18   0.860    -.1640188    .1369858
        year |   .1024004   .0782997     1.31   0.191    -.0510642     .255865
    location |   -.138701    .075597    -1.83   0.067    -.2868683    .0094663
 environment |   .3434337   .1299966     2.64   0.008      .088645    .5982224
        time |  -.2548438   .1269314    -2.01   0.045    -.5036248   -.0060628
 opportunity |   .0961225    .079104     1.22   0.224    -.0589185    .2511636
------------------------------------------------------------------------------

请问各位大虾，我的社会经济变量为什么在回归中都被omitted了呢？clogit中怎么考虑相关的社会经济变量阿