Duds and rock stars are easy to spot. Here’s an assessment system to help ensure that you don’t hire the candidate who’s almost good enough.

All of the best recruiters I know use performance-based job descriptions and follow this three-part guide to hiring when assessing candidates:

Rule One: Suspend judgment for at least 30 minutes. A good first impression may compel you to seek out evidence to justify a hire, and the opposite is true for candidates who begin on the wrong foot. Counteract this natural reaction by focusing on gathering specific evidence of exceptional performance during the work-history review.

Rule Two: Probe for an “achiever pattern” indicating the candidate is in the top 25 percent of his or her peer group. Specifically, look for the following:

1. People who change jobs in order to propel career growth, not seek security or avoid problems

2. A consistent pattern of taking on difficult technical projects beyond their experience level. Managers assign their best people to tackle the trickiest challenges for a reason.

3. A history of volunteering for risky assignments that stretch skills. Success builds confidence.

4. Early-career exposure to senior executives and important projects.

5. Important jobs on multi-functional project teams. Be wary of people whose team growth plateaued early.

6. A track record of being promoted ahead of peers. Award double bonus to candidates who did so at different companies and with different managers.

7. Company or industry recognition in the form of awards, honors, advanced educational opportunities, or speaking engagements.

Rule Three: Use the information gathered in that first 30 minutes to rank candidates according to the performance-based scale below. Note that it is a nonlinear scale — in other words, Level 3 is reserved for the top 25 percent of people doing similar work. These are not C students; they are great hires.

From a practical standpoint, it’s impossible to accurately assess a person in 30 minutes. However, half an hour is plenty of time to identify your Level 1s and Level 5s. Everyone else will fall in the Level 2-4 range. You should spend the next hour or two of the interview trying to make sure you don’t hire a Level 2.

Avoiding the 1s is easy. You have to dig deep to avoid hiring a Level 2. Here is what you’re looking for:

Level 1 — Bottom Third: This candidate has neither the skills nor the motivation to do the work at a consistent level of quality. He or she gets hired when the interviewer emphasizes personality or first impressions, and fails to conduct due diligence (i.e., reference checking, background verification).

Level 2 — Bottom Half: This candidate has the basic skills to do the work, but is not highly motivated. Suss this out by asking where the person took the initiative, went the extra mile, or volunteered to lead an important project. If you don’t find much, categorize the person as a Level 2. These people get hired by box-checking skills and riding the coattails of first impressions or intuition.

Level 2.5 — Average: There is little evidence the person is out-performing his or her peers on any factors.

Level 3 — Top 25%: This person demonstrates an “achiever pattern” indicating that she has been recognized by colleagues as a top performer and a promotable person.

Level 4 — Top 5-10%: It’s nearly impossible to determine whether someone is a Level 4 in just 30 minutes. Clues include getting some major company award like a fellowship, a special grant, extraordinary bonus or special assignment.

Level 5 — Rock Star, Top 1-5%: Rock Stars typically have a track record of rapid promotions in different situations, always being assigned to the most important projects and succeeding, or receiving industry-wide recognition.

Follow the “No 2s” rule to ensure everyone you hire is a Level 3, 4 or 5. Some will be all-stars, some will be MVPs, and everyone else will make the starting team.