Implicit Hiring Criteria

At Thread I’m involved in hiring engineers for frontend, backend and iOS roles. One of the things I have become more aware of as I have gained experience in hiring and interviewing is how my biases affect the outcomes of interviews. This is something I’m always trying to improve – to understand what biases I have, to mitigate their effects – and in the process I have found a mental model that has helped me.

Hiring, and scoring candidates, is usually framed around criteria or competencies, that we are explicitly hiring for, but this is only one of 4 categories of of assessment criteria.

It follows that if there are things we are hiring for, there must therefore be things we aren’t hiring for. Additionally, if there are things we are explicitly looking for, there may be things we are implicitly looking for.

We can draw up a table to explore all of these cases.

Looking for Not looking for
Explicit (1) Competencies, the skills we’re seeking for this role (2) Limits to what we are looking for
Implicit (4) Things we require from candidates without knowing it (3) Things we don’t realise are important to the role

Let’s look at each of these in detail. We’ll go by the numbers above as this will help us to get a full understanding of the model.

1. Explicitly looking for

This is the easiest, it’s our traditional criteria or competencies. Let’s use an (infamous) example: asking a software engineer to write the algorithm for reversing a binary tree on a whiteboard. In this case the criteria may be:

  • Candidate is able to parse and understand a problem description.
  • Candidate can produce working code to solve a straightforward problem.

These are reasonable criteria for a software engineer, and while this particular interview has its problems, it is likely to give us some signal on these criteria that will help us decide if the candidate is suitable for the role.

This category of requirement is the basis of all hiring, and well understood.

2. Explicitly not looking for

This category of criteria is sometimes used, but in my experience could often be used more. Essentially we’re asking what attributes are not important for us in a candidate. A concrete example of this is in the pair programming interview I do with candidates at Thread.

We have decided as a team that we are not looking for Python engineers, and that we believe that a good engineer will become a good Python engineer regardless of whether they already know Python or not.

For backend engineers I run this interview in Python, as I have a good understanding of what is possible in the solutions. However because we have decided that Python is something we are explicitly not looking for, I know to exclude certain kinds of missteps a candidate might make from my assessment. I also know that I should provide as much help as I can on Python syntax and understanding without penalising candidates.

Being clear within the hiring team about what is not important means more alignment in the hiring team, and fewer opportunities for bias to creep in. A good way to achieve this is with explicit rubrics for interviews.

3. Implicitly not looking for

These are criteria that we haven’t realised are needed for the role, and therefore aren’t assessing for.

For example, how much of a software engineer’s role is writing code, and how much is tech meetings, email, reviewing code, explaining technical topics, and other forms of communication? Are we assessing for communication at all, or in enough detail?

Another example of this may be culture fit. Many companies assess for this badly and introduce bias into their process, but when this is done well it can result in a team that is diverse on most axes, but has a shared set of agreed upon values.

  • Does the team value collaboration, or value individuals going deep on topics by themselves?
  • Does the team value craft and reliable engineering, or does it value moving quickly and responding to changing priorities?
  • Does the team value performance or readability of code?
  • Does the team value a theoretical approach, or a practical one?

These are all on a spectrum (as well as being simplifications to illustrate a point), with very few teams falling completely at one end. All teams will have different views on what’s important and by understanding these views, and interviewing for engineers whose views align, it’s possible to build a team that works well together. It’s important to note that this can be a way to unknowingly introduce bias into your hiring, so this needs to be done carefully.

4. Implicitly looking for

This is the category I find most interesting, and the one I have learnt the most about since I started interviewing.

For an example, let’s return to our whiteboard test from before. While there are a few criteria that we want to assess with this, there are also some hidden criteria we may not realising we’re assessing:

  • Can the candidate speak in front of a (small) audience?
  • Does the candidate know specifically what a binary tree is and how to reverse it?
  • Is the candidate physically able to write on a whiteboard?

It’s easy to explain these away…

You can ask questions and figure out roughly what a binary tree is if you don’t know it already, and who doesn’t know it anyway?!

Not everyone comes from a Computer Science degree, some people may have come from web design, games testing, QA, IT, etc. They may never have learnt what a binary tree is, at least not enough to remember confidently in an interview context. Is this really important for the role? It may be, but it’s important to make an explicit decision, rather than fall into an implicit one.

Who isn’t able to physically write on a whiteboard? If they can’t, they’ll just say so.

Candidates with dyspraxia may struggle to write on a whiteboard. Assuming that a candidate will push back on an aspect of an interview if they have a reason to is a big assumption – interviews have strong power dynamics that people deal with in very different ways.

Another good example of things implicitly sought in interview processes is with take-home tests. These are often open ended, which selects for candidates who have significant free time to spend on the test. Is having lots of free time a necessary criteria for the role? Probably not, and so it’s important to not make it an implicit criteria.

It’s important to know what skills an interview is implicitly selecting for. Are they really important?


I think all criteria being assessed in interviews will fall into one of these four categories. Which one will depend on the role, the team, the interviewers, but there’s one approach I think everyone could benefit from: make everything explicit.

By trying to find what’s implicit in your current process and making it explicit, you may have the opportunity to further refine your job spec, further understand what you’re looking for, and further eliminate bias from your process. It’s not easy to find the implicit criteria, but it can be made easier by talking to candidates, having retrospectives in the hiring team after each candidate, using resources such as Hire More Women In Tech, and constantly iterating your hiring descriptions and interview rubrics.

This is certainly not a catch-all solution to biases and diversity in hiring, but it is a mental model that I have found useful to help improve my understanding of the topic and improve how I interview.