(A prerequisite for this article is conducting a thorough job analysis and defining success criteria.)
The quality of employee performance begins with the quality of the hiring process. The first step in evaluating candidates is to make sure that you observe and document behavior during the interview. Write down important behaviors described by the candidate as soon as they occur and document only those behaviors that occur during the interview session. Do not evaluate during the interview - your role during this phase is to record and capture all relevant candidate responses.
Be careful about making inferences and conclusions about the candidate. If you do write down an inference or a conclusion (e.g., unorganized, not assertive), you should always support that inference or conclusion with a relevant descriptive behavior (e.g., ignored critical deadlines and did not communicate upcoming dates with her team, did not ask customers probing questions to get the whole picture). Relevant behaviors should be used as the basis for evaluations, not conclusions about vague traits or characteristics unrelated to the job.
Be aware of common rating errors and interviewer biases which may influence our judgment process. Some of the most common are halo effects (judging a candidate strong in many areas because he or she is strong in one area), stereotyping (judging a candidate because of the people or group with whom he or she is associated), similar-to-me (judging a candidate because he or she is believed to be like the interviewer), and central tendency (viewing all candidates as "middle of the road").
For each job success factor pursued in the interview, use performance standards and success criteria developed with the aid of subject matter experts to help you make accurate evaluations. This way, candidates will be evaluated by comparing their behavior against evaluation criteria, not against each other! Align the evaluation criteria with a traditional Likert scale of 1-5 or 1-3 with 5 or 3 equaling the highest performance. Behaviorally define each evaluation point (e.g., 1, 2, 3, etc.) with a performance description. Review your interview notes and compare the candidate responses to the Likert scale, noting the performance level of the behaviors (e.g., 1, 2, 3, etc.). Assign a numerical rating for each success factor.