Researchers gave white college students two resumes in an experiment in which they were asked to play the role of an employment officer. The resumes were desighed to have equal qualification, but one had a photo of an african american attached and the other had a photo of a white applicant. The researcher found that there were no significant differences between the evaluations of the black applicant and the white applicant. Why can't the researcher conclude that the student's judgments were not influenced by the race of the applicant? list confounding variable and how they can be eliminated?