Why does BCG only include full and part-time permanent employees?

It is important to stay with our policy of not interviewing the non-traditional employees. Short term employees typically do not have a strong understanding of the organization, do not receive benefits, and are not mentally “invested” in the way that full-time and permanent part-time employees are. Their opinions may not be representative of the organization’s culture and these employees may artificially impact the evaluation (either positively or negatively).