To the best of my knowledge it has no effect whatsoever. You are asked this information to help the government keep track of how many blacks, Asians, females, Mexicans etc work in what type on industries. They are looking for other characteristics to consider employing you. They can tell what color you are from interviewing you or from other demographic characteristics.I am one of the few people who has been successful in every single job interview I have ever attended. This is because I volunteer information that my prospective employer may be barred from asking. I volunteer the fact that I am extremely healthy as evidenced that I have participated in three marathon races. I volunteer the fact that I have a perfect attendance record with my previous employers. I volunteer the fact that I have perfect credit rating. Finally I prdocumentation to prove it.