Dear Statalist
I am currently using Stata 12.
I have a set of dichotomous variables that I'm using to predict a categorical outcome in logistic regression. However, one of the independent variables (BAND where 1 = yes, 0= no) has no observations for the category 0. Accordingly, stata provides the following message:
TR_BAND != 0 predicts success perfectly
TR_BAND dropped and 8 obs not used
I understand why this is happening i.e., the model cant be fitted because the coefficient for BAND is negative infinity (since the dependent variable doesn't vary within the Band = 0 category).
So effectively, Stata's solution is to drop that variable and all observations where Band =1,
My question is:
1. Should this model be fitted at all (i.e., should I proceed to analyze the results of this model that stata modified by dropping the foregoing variable?)
2. Would it make sense/ be defensible, alternatively, to remove the problematic variable (BAND) from the model apriori-- before running the logistic regression? (in this case, we would be preserving the observations and hence sample size).
3. A reviewer has pointed out that since the variable is excluded from the model, the logistic regression analysis should not even be performed at all. Is he correct? Should the model not be fitted at all? OR if he is incorrect, how do I assuage his concerns about interpreting a model where the variable BAND has been excluded?
thank you!
Katherine Picho
I am currently using Stata 12.
I have a set of dichotomous variables that I'm using to predict a categorical outcome in logistic regression. However, one of the independent variables (BAND where 1 = yes, 0= no) has no observations for the category 0. Accordingly, stata provides the following message:
TR_BAND != 0 predicts success perfectly
TR_BAND dropped and 8 obs not used
I understand why this is happening i.e., the model cant be fitted because the coefficient for BAND is negative infinity (since the dependent variable doesn't vary within the Band = 0 category).
So effectively, Stata's solution is to drop that variable and all observations where Band =1,
My question is:
1. Should this model be fitted at all (i.e., should I proceed to analyze the results of this model that stata modified by dropping the foregoing variable?)
2. Would it make sense/ be defensible, alternatively, to remove the problematic variable (BAND) from the model apriori-- before running the logistic regression? (in this case, we would be preserving the observations and hence sample size).
3. A reviewer has pointed out that since the variable is excluded from the model, the logistic regression analysis should not even be performed at all. Is he correct? Should the model not be fitted at all? OR if he is incorrect, how do I assuage his concerns about interpreting a model where the variable BAND has been excluded?
thank you!
Katherine Picho
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