Although it can be tempting to give candidates an overall score of your impression, research shows that a structured interview with preset questions is 34% more effective at predicting job performance than an unstructured interview. The reason for this is that unstructured interviews are not standardized, and interviewers who use them fall prey to confirmation bias. Studies by Frank Bernieri at the University of Toledo have found that interviewers without set questions will form an opinion about the candidate in the first 10 seconds of the interview, and spend the rest of the interview confirming these biases.