Interviewers who don’t have an accurate picture of what the job entails and what sort of candidates best suited for it usually make their decisions based on incorrect impressions or stereo types of what a good applicant is. They then erroneously match interviewees with their incorrect stereo types.
One classic study involved 30 professional interviewers. Half got just brief description of the jobs for which they were recruiting: they were told the eight applicants here represented by their application blanks are applying for the position of secretary. The other 15 interviewers got much more explicit job information, in terms of typing speed and bilingual ability, for instance.
More job knowledge translated into better interviews. The 15 interviewers who had more job information generally agreed among themselves about each candidate’s potential, while those without complete job information did not. The latter also didn’t discriminate as well among applicants they tended to give them all high ratings.