Hmm. I whipped up a quick python script to test this theory.

  Age,Hours Wrkd,Income was unique ~89% of the time
  Age,Hours Wrkd, Yrs in industy,Income was unique 97% of the time
  Age,Education,Hours Wrkd,Income was unique 94% of the time
  Age,Education,Hours Wrkd,Yrs in Industry,Income was unique 98% of the time

Here it is if anyone wants to play with it. http://paste.pocoo.org/show/136649/