The well-known expression professional bias appears to date back to the very first years when professions started to exist:
- "Professional bias" designates a mental conditioning brought about by the particularities of one's job. A contrived example is that of a race-car driver, say, who overtakes dangerously when he's out driving in the family automobile with his wife and kids.
Ngram shows that the expression was first used towards the end of the 18th century, roughly during the same years when the first professions were born.
early 15c., of religious orders; 1747 of careers (especially of the skilled or learned trades from c.1793); see profession. In sports, opposed to amateur, from 1846.
professional (n): "one who does it for a living," 1798, from professional (adj.). (Etymonline)
Was the expression coined with the birth of the first professional activities in England or did it already exist in religious contexts where the term profession seems to come from.