Currently I am doing choice experiment modelling using conditional logistic model. I am treating all of my attributes as categorical variables. Therefore I run this command using Stata14:
clogit most i.benefit i.distribution i.duration i.restriction i.participation, group(respqu)
However, I got this response:
note: 3.distribution omitted because of collinearity
note: 6.duration omitted because of collinearity
note: 1 group (3 obs) dropped because of all positive or
all negative outcomes.
Iteration 0: log likelihood = 2544.1899
Iteration 1: log likelihood = 2463.2558
Iteration 2: log likelihood = 2459.202
Iteration 3: log likelihood = 2459.1952
Iteration 4: log likelihood = 2459.1952
Conditional (fixedeffects) logistic regression
Number of obs = 8,106
LR chi2(10) = 1018.51
Prob > chi2 = 0.0000
Log likelihood = 2459.1952 Pseudo R2 = 0.1716

most  Coef. Std. Err. z P>z [95% Conf. Interval]
+
benefit 
500  1.019902 .0955277 10.68 0.000 .8326708 1.207133
1000  1.347354 .094481 14.26 0.000 1.162174 1.532533
1500  1.353202 .093054 14.54 0.000 1.170819 1.535584

distribution 
1  .2844393 .0608707 4.67 0.000 .1651349 .4037437
2  .368224 .0605038 6.09 0.000 .2496387 .4868093
3  0 (omitted)

duration 
2  .0632722 .0603698 1.05 0.295 .1815948 .0550505
4  .0115473 .0621341 0.19 0.853 .133328 .1102333
6  0 (omitted)

restriction 
1  .6369584 .0605884 10.51 0.000 .7557095 .5182074
2  .7518877 .0610098 12.32 0.000 .8714646 .6323107

1.participation  .4798952 .0444267 10.80 0.000 .3928205 .56697

I found 2 variables from 2 attributes are omitted (distribution 3 and duration 6). When I added status quo variable, the variable is omitted as well, and the response are not changed. I need to keep those 2 variables since all are important. Could somebody give me advice please to solve this problem?? Your advice is appreciated. Many thanks.
clogit most i.benefit i.distribution i.duration i.restriction i.participation, group(respqu)
However, I got this response:
note: 3.distribution omitted because of collinearity
note: 6.duration omitted because of collinearity
note: 1 group (3 obs) dropped because of all positive or
all negative outcomes.
Iteration 0: log likelihood = 2544.1899
Iteration 1: log likelihood = 2463.2558
Iteration 2: log likelihood = 2459.202
Iteration 3: log likelihood = 2459.1952
Iteration 4: log likelihood = 2459.1952
Conditional (fixedeffects) logistic regression
Number of obs = 8,106
LR chi2(10) = 1018.51
Prob > chi2 = 0.0000
Log likelihood = 2459.1952 Pseudo R2 = 0.1716

most  Coef. Std. Err. z P>z [95% Conf. Interval]
+
benefit 
500  1.019902 .0955277 10.68 0.000 .8326708 1.207133
1000  1.347354 .094481 14.26 0.000 1.162174 1.532533
1500  1.353202 .093054 14.54 0.000 1.170819 1.535584

distribution 
1  .2844393 .0608707 4.67 0.000 .1651349 .4037437
2  .368224 .0605038 6.09 0.000 .2496387 .4868093
3  0 (omitted)

duration 
2  .0632722 .0603698 1.05 0.295 .1815948 .0550505
4  .0115473 .0621341 0.19 0.853 .133328 .1102333
6  0 (omitted)

restriction 
1  .6369584 .0605884 10.51 0.000 .7557095 .5182074
2  .7518877 .0610098 12.32 0.000 .8714646 .6323107

1.participation  .4798952 .0444267 10.80 0.000 .3928205 .56697

I found 2 variables from 2 attributes are omitted (distribution 3 and duration 6). When I added status quo variable, the variable is omitted as well, and the response are not changed. I need to keep those 2 variables since all are important. Could somebody give me advice please to solve this problem?? Your advice is appreciated. Many thanks.