Why do I have to log in when answering a survey on Kiosk mode?

Question 

Why do I have to log in when answering a survey on Kiosk mode?

Answer

When answering your survey using kiosk mode, you will be asked to login to the survey using either a unique code or your employee ID and first name. Your scores and comments remain confidential but a login is needed to ensure that the same survey cannot be answered twice by the same employee, and to measure the overall survey participation rate for each survey round. 

Managers are not able to see which employees have answered or not, they will just see the percentage of employees who have answered.