HR managers have to be fair and objective, and put aside any assumptions, stereotypes, and prejudices when going through the hiring process. But alas, we are human. We can be charmed by a charismatic job candidate, or completely dismiss someone whose interviewing skills are unpolished. Essentially, we jump to conclusions often without even realizing it.
Here are a few common mistakes to look out for when you're interviewing:
Similarity or dissimilarity bias
Giving a higher priority to candidates with whom you have something in common (same alma mater, same hobbies, same personality, etc.).
Ignoring negative qualities or lack of skill because you like the person.
Focusing on a personality trait that you don't like in people, even though it's not relevant to the job, and discounting a candidate as a result (person is too opinionated, highly extroverted or highly introverted).
Giving too much weight to first impressions. Consider this: 50% of first impressions are based on appearance!
Generalizing a strength or weakness in one area to other areas. For example, you get so excited by a candidate's amazing technical skill, that you assume he also has the soft skills to lead people. Or a candidate mentions that she focuses best when working on her own, and you assume she won't be a team player.
Automatically faulting or entirely dismissing candidates who don't do well during the interview. What you may not realize that the person might be nervous, inexperienced with the interview process, or at a disadvantage when coming up with responses on-the-spot, but skilled at planning or coming up with ideas when given time to think.
Ignoring cultural issues/biases. People in some cultures are raised to be humble, and won't flaunt or talk about their accomplishments. Moreover, if English is not a person's first language, he or she may misunderstand some questions, or common English idioms.
Primacy and recency effects: This refers to the tendency to remember more details about the first and last candidate interviewed.
Problematic interviewing techniques
Not digging deeper by asking follow-up questions ("Are you detail-oriented?" Follow up: "Yes? Can you describe a project where your meticulousness came in handy?").
Allowing first impressions to impact the type of questions you ask. For example, if the candidate seems very assertive, you might ask: "Have you ever had difficulty with a client or colleague because you came on too strong or in an opinionated manner?"
Screening out people who have the right personality but don't exactly meet skill requirements. Remember, if they have the right aptitude and their skills gap is not too large, they can be trained.