From the DOT Publication Best Practices for Random Drug and Alcohol Testing.
“Is the boss singling me out? I just did a random last month? Joe, never gets tested? I don’t think this thing is random at all!” Those are not uncommon concerns among some safety-sensitive employees, and many employers have been challenged in court to demonstrate that their programs are truly random. The reality is that in a truly random selection process, a high probability exists that some employees will be selected several times while others may never be selected. Why? Because after each selection, the employee’s name is returned to the same pool, and he or she becomes just as likely as anyone else to be selected next time.