Fundamentals of Interviewing

Advice regarding interviewing often devolves into descriptions of an author's favourite interview method with no justification as to why it's preferable. For example I've read advice that promoted developing a holistic view of each candidate. It sounds smart on the surface but fundamentally has no connection to the goals of interviewing. This article describes the fundamental goals of interviewing so you can better reason about interview methods.

Evaluation

The primary objective of interviewing is to produce an evaluation of the candidate's objective quality. Usually an evaluation is binary: pass/fail. Some frameworks involve greater granularity but all evaluations are one-dimensional. The following properties determine the quality of an evaluation, i.e. whether the interviewer did a good job or not.

1. The evaluation has a positive correlation with candidate quality
2. The evaluation can be compared to other evaluations

The first property is obviously important. Candidate quality is the cumulative net business value the candidate would provide the company if hired. Accepting this definition does not require you subscribe to a world view where people have a measurable objective worth, only objective business value.

The second property is required for the evaluations to be useful in making hiring decisions. Evaluations that cannot be compared are useless to hiring managers.

Let's appreciate for a moment properties that are not fundamentally required. The evaluation need not necessarily be justified in any way although practically speaking to correlate with candidate quality there has to be some touch point with reality. The evaluation also needs not be nuanced. It's explicitly the complexity of a human person reduced to a one-dimensional score.

Note that an evaluation is not the same as making a hiring decision. Hiring managers usually use multiple evaluations to make decisions. The evaluations are just one tool to help them make decisions. An interviewers job is not to decide whether a candidate should be hired or not.

Secondary Objectives

Producing an evaluation is the driving motivation for conducting an interview in the first place. Secondary objectives are a side-effect of interviews not happening in a vacuum. Since interviews interact with the rest of the world it's preferable the interactions are positive.

Providing a positive candidate experience leads to positive outcomes for the company as well. Candidates influence other prospective candidates in their networks. They might also wish to apply again in the future. Providing a positive candidate experience means you get more future applications and protect your company's reputation.

Another secondary objective is to minimize the cost of interviewing. Usually the greatest cost is the interviewers' time so reducing the duration of interviews and number of interviewers provides immediate savings.

Notice the objectives can conflict. Enumerating the objectives explicitly helps reason about trade-offs. You can justify an interview method by arguing it serves one of the objectives without hurting the others too much.

Feedback

Interviewers get immediate feedback on how well they are doing with regard to the secondary objectives. However, interviewers seldom get any feedback on the quality of their evaluations. Couple this with the lack of advice and the fact interviewing is usually a secondary task for an interviewer, not what they were hired to do.

An interviewer who does not consciously seek to improve their interviewing skills will naturally adopt behaviours that serve the secondary objectives at the expense of the primary objective. Interviewers can save time by skipping preparation for an interview and if they're never held accountable this behaviour will not be corrected. More insidiously, interviewers can adopt behaviours that make them feel better during an interview, such as providing excessive assistance to a candidate or interpreting answers to fit their own biases.

The lack of feedback means experience alone will not naturally teach interviewers to be better at the task. Interviewers must deliberately seek to make good evaluations. Luckily interviewers, like most people, generally want to do a good job even if they aren't held accountable. Simply making interviewers aware of what makes an evaluation good will remedy most of the bad behaviour described above.

Practice

From the fundamental objectives we can derive more practical principles such as the following.

1. Reduce bias as much as possible. Biases reduce the correlation between candidate quality and evaluation.
2. Make the interview process fast. A faster process is less costly and less cumbersome to candidates.
3. Make the interview process appear fair. Candidates who perceive a rejection to be their own failing have a better experience than candidates who attribute it to luck or the interviewer.

These are still really generic but you can justify specific interview methods with them. For example a repeatable process such as using the same interview questions for all candidates reduces bias. Cutting out interview questions that don't help make an evaluation shortens an interview. Using an interview process that candidates can reasonably expect feels more fair than something bespoke.

Any piece of interviewing advice can be evaluated by considering whether it contributes to the fundamental objectives. For example advice about forming a holistic view of a candidate is entirely unrelated to the objectives. It's not actively harmful but it's not helpful either. Question each aspect of your interview process and try to answer how it contributes to one of the objectives. If you can't come up with an answer you've identified an area for improvement.