hi all,

In the xtlogit regression below

(All variables in this regression are dummy variables.)

1. Why have this data been

2. What features did these data have?

3. Is it possible that the selection bias has occurred despite the dropped of most of the data?

In the xtlogit regression below

**17667 groups**of data have been**dropped**.(All variables in this regression are dummy variables.)

1. Why have this data been

**dropped**?2. What features did these data have?

3. Is it possible that the selection bias has occurred despite the dropped of most of the data?

Code:

. xtlogit underline L.q L.underline,fe note: multiple positive outcomes within groups encountered.note: 17,667 groups (35,334 obs) dropped because of all positive or all negative outcomes.Iteration 0: log likelihood = -1074.9136 Iteration 1: log likelihood = -939.89854 Iteration 2: log likelihood = -937.31563 Iteration 3: log likelihood = -937.09315 Iteration 4: log likelihood = -937.09076 Iteration 5: log likelihood = -937.09028 Iteration 6: log likelihood = -937.09019 Iteration 7: log likelihood = -937.09019 Conditional fixed-effects logistic regression Number of obs = 5,014 Group variable: Address Number of groups = 2,507 Obs per group: min = 2 avg = 2.0 max = 2 LR chi2(2) = 1601.26 Log likelihood = -937.09019 Prob > chi2 = 0.0000 ------------------------------------------------------------------------------ underline | Coef. Std. Err. z P>|z| [95% Conf. Interval] -------------+---------------------------------------------------------------- q | L1. | .0356927 .1197559 0.30 0.766 -.1990246 .27041 | underline | L1. | -20.42288 798.6675 -0.03 0.980 -1585.782 1544.937 ------------------------------------------------------------------------------

## Comment