If you understand real job needs, you only need to ask two questions to predict on-the-job success. It doesn't matter what you ask if you don't know job needs, you'll either be wrong, or lucky.
It took me 30 years and 2,500 interviews to make this table showing the best and worst predictors of on-the-job success. Since I've had the opportunity to work with people I've placed after they were hired and with candidates who were excluded, I can say with the utmost confidence that most interviewers are biased and few have a clue on how to interview properly.
The problem starts by using laundry lists of skills and competencies to screen candidates and then asking a hodgepodge of supposedly clever questions to confirm the interviewer's initial biased reaction to the candidate. These emotional feelings are then voted on using thumbs with the biggest thumb winning the yes/no decision contest.
This rather cynical view is justified if you've ever been involved in these types of ego contests masquerading as judgment.
There is a better way.
First, throw away the laundry list of skills and competencies and define the job as a series of 5-6 performance objectives describing the task, the action required to complete the task and some measure of success. For example, "Reduce scrap on the widget line from 5% to less than 1% by year-end," is a lot better than saying, "Must have 10+ years of high-volume widget production experience, an engineering degree from a top school, a results-oriented attitude and enough EQ to get hugs from the entire team."
Once you put your list of performance objectives in priority order ask the candidate this question, "Can you describe your most significant career accomplishment related to (reducing scrap)?" Spend about 15 minutes on this question, gaining insight into the results achieved, the competencies and skills used, the environment and culture, and the process used to achieve the results. Then ask this same question again for all of the other performance objectives. This will determine fit with the job and if you plot the accomplishments over time the trend line reveals consistency, growth and potential.
The second question is entirely different. It goes something like this:
"One of the biggest challenges in this job is (provide short description). If you were to get the job, how would you go about solving it?"
For the widget example, the question might be, "We have a big scrap problem. Can you walk me through how you would figure out the root cause and put together a solution?"
Asked properly this question uncovers a critical ability of all top performers: job-related problem-solving skills. The best candidates I've met in my 35 years in executive search all have the ability to anticipate the needs of the job before starting it. They can figure out very quickly what's wrong or what's necessary to accomplish a task, what they need to do to implement a solution, and what resources they need to do it. Even better, they "see" the problem, the solution, and the steps needed to get there. They also know what they don't know and are confident enough to tell you how they'll get this information.
When you ask this problem-solving question it's important to turn off the spotlights and shift the conversation into a more natural give-and-take discussion about real job needs. This way the meeting is no longer an interview but a business-like discussion with a team member trying to work together to figure out a solution to a real problem. Once you get comfortable with this style of interviewing, you'll be able to assess the following four dimensions of thinking skills.
The Four Dimensions of Thinking and Problem-solving
Depth. Determine if the reasoning is complex, advanced or superficial. The best candidates demonstrate a good understanding of the cause and effect of a problem and can determine how to find the root cause. Superficial reasoning is evidenced by a bunch of seemingly unrelated or more generic ideas.
Focus. Is the focus technical, tactical, or strategic? Candidates with a pure technical focus get into process or concept details. Those with a tactical bent address the results and outcomes more. A strategic focus is represented by a longer time horizon with consideration to the implications and the unintended consequences.
Team or individual emphasis. Understand if the candidate's ideas and approaches involve others or if the person is more individual or self-focused. This is an important consideration if the person will be managing others or involved in a number of team projects.
Functional or multifunctional perspective. The best candidates understand the implications of their job on other people and other functions. Listen for this as the candidate plans out his or her tasks and asks questions.
Use the Anchor and Visualization Technique to Increase Interviewing Accuracy
Often people can talk a good game but can't deliver the results. To address this concern, just ask this question after the candidate has answered the problem-solving question, "Now can you tell me about something you've accomplished that's most related to what we need done?"
I refer to this two-question combination as the Anchor and Visualize approach. A track record of past performance and the ability to visualize the future is a great indicator of ability. When combined with a clear understanding of real job needs using a performance-based job description, these two questions are all you need to ensure you're hiring a great person.