All the data are in. We checked for errors during entry, but errors are still in. Now we must cross check all variables; Are the extreme values reals or result of mistakes?. Are the correlations between critical variables plausibles or one of the questions was obviously misinterpreted? If we find some errors we must take a decision:
a- we eliminate the record from the corresponding analysis.
b- we impute a new value to replace the one in error.
There are several acepted techniques for imputation, but the decision whether to impute or not depends on the number of errors, if they are very few, or many, we better eliminate the records with errors, otherwise we impute a new value.