I have heard people say “I am not prejudicial.” I say “Then you are not sane.” Prejudice and bias are often confused. We are all prejudiced. It is part of the human condition. Prejudice is “pre” judging based on our expectation. Bias is judging contrary to facts or slanting the interpretation of facts.
An example: In 1950 my father bought a Ford car. The ash tray was made from stamped metal with a sharp corner that ripped his pants one day. From that time on, he would not consider a Ford. Later when Ford started a quality campaign and improved quality – he still would not consider the car based on his experience decades before. He became loyal to solidly built Chrysler cars. When I bought a fleet of Plymouth cars that had numerous problems (loose oil filter fell off one car within 50 miles of purchase, another seat belt retainer pulled out of door frame on first use and a host of numerous other problems) he still claimed they were superior quality to Fords. He was prejudiced against Ford and for Chrysler based on experience. He was biased when the facts changed and he held his prejudicial view.
Another example: When I retired the first time, I applied for a another job. The interview stressed knowledge of computer skills and some of the problems the organization was having with their Wang inventory control program. They wondered if a person of my age would be up on computers (age discrimination and prejudice). Need less to say I was not hired in spite of the fact that I had with a programmer assigned to me, written a much more sophisticated inventory control program years before they became fashionable and in the next job for which I was hired wrote an internal program by myself that was more complex and more functional, lower cost to administer, as well as lower cost to update/modify.
A psychological experiment showed a picture of a white man in a police officer embattled with a black man. Subjects were asked to comment on the picture. Whites tended to describe it as a black criminal resisting arrest. Blacks viewed it as police brutality. Either or neither may be true. In fact we assume the man in uniform was a real police officer and that the black man was a criminal and was not an undercover officer. It could have been. The point is we based our decision on our predisposition and the assumptions that predisposition leads to.