Experiments have shown that in selecting personnel for a job, interviewing is at best a hindrance and may even cause harm. These studies have disclosed that the judgments of interviewers differ markedly and bear little or no relationship to the adequacy of job applicants. Of the many reasons why this should be the case, three in particular stand out. The first reason is related to an error of judgment known as the halo effect. If a person has one noticeable good trait, their other characteristics will be judged as better than they really are. Thus, an individual who dresses smartly and shows self-confidence is likely to be judged capable of doing a job well regardless of his or her real ability. The horns effect is essentially the same error, but focuses on one particular bad trait. Here the individual will be judged as incapable of doing a good job.
Interviewers are also prejudiced by an effect called the primacy effect. This error occurs when interpretation of later information is distorted by earlier connected information. Hence, in an interview situation, the interviewer spends most of the interview trying to confirm the impression given by the candidate in the first few moments. Studies have repeatedly demonstrated that such an impression is unrelated to the aptitude of the applicant.
The phenomenon known as the contrast effect also skews the judgment of interviewers. A suitable candidate may be underestimated because he or she contrasts with a previous one who appears exceptionally intelligent. Likewise, an average candidate who is preceded by one who gives a weak showing may be judged as more suitable than he or she really is.
Since interviews as a form of personnel selection have been shown to be inadequate, other selection procedures have been devised that more accurately predict candidate suitability. Of the various tests devised, the predictor that appears to do this most successfully is cognitive ability as measured by a variety of verbal and spatial tests.