# Can identifiers be used to train a model?

I recently participated in some Machine Learning competition where we were asked to decide whether a rider should accept or not a course (~2k riders and ~140k courses). It came up that some of the winners used the identifier of the rider (an integer number unique for each rider) in their features which was discarded on default notebook and it greatly improved their score.

Is it legitimate? can identifier be used to train a model?

• Share more information on identifiers. Is it unique or having any pattern ?? – Wickkiey Apr 12 at 13:46

You can use any variable during model training if this variable is available during inference time. This is the only technical restriction. Another question is should you include this column or not. If this column is completely unique and does not have any relevant information in it then you can discard it. Also, categorical columns with high cardinality (number of unique values) might also have a negative impact.