What the maths of dating can tell you about recruitment success rates

Are dating and recruitment similar? Brendan O’Donovan, Hays’ Group Data Marketing Director, delves into the data.

Recruitment success rates: Key insights

The challenge of dating is that you can’t know for certain whether your current date is going to be the best suitor you’ll ever find. Settle down too quickly, and you might never meet Mr or Mrs Perfect. Get too picky, and you may end up rejecting someone who is highly suitable for you. 

Replace the word “suitor” with “the perfect job candidate”, and you will see that there are in fact many parallels between dating and recruitment. Albeit, admittedly, with very different judging criteria.

According to plus.maths.org the strategy is simple: “Out of all the people you could possibly date, see about the first 37 per cent. Then after you have dated the first 37 per cent, settle for the first person who’s better than the ones you saw before.” 

In other words, multiply the number of different dates you go on each year by the maximum number of years before you’d want to settle down. Then date 37 per cent of this number. Pick your best date from the 37 per cent (let’s call them person a), and then continue to date the remaining 63 per cent until you find someone better than person a.

While this sounds like a cut-throat approach to love, could it work for recruitment?

Recruitment success rates: Background

There’s a problem with the 37 per cent theory when hiring. Unfortunately, while this simplified problem has a very elegant mathematical solution, it isn’t a lot of help in the real world of hiring. Specifically, there are three big issues with the way it’s set up:

1. No search costs - For dating, it might not matter if you spend the whole of your twenties working your way down the list to the magic 37 per cent. But, in a real business, there are time costs involved in recruiting. Think about the time taken away from the hiring manager for each interview, and the cost of leaving a vacancy open longer than needed. Time many might not be able to afford.

2. Focus on perfection – As presented, the only thing that the 37 per cent rule cares about is maximising your probability of landing the single best person. The rule doesn’t care if the best person turns up in the first 37 per cent. In fact, it specifically states you should still reject them.

In the real world, failing to fill a role can be very damaging. We know that of all the account directors or software developers in the world, it’s not realistic to try to find the single best one. So, a more realistic objective might be to maximise the probability of hiring someone in the top 10 per cent of performance for that role.

3. No going back – In dating, the idea that you usually can’t go back makes some sense. In recruitment, the idea that you would interview and then accept or reject people precisely in a sequence is clearly unrealistic. 

In the real world, candidates are interviewed in parallel. You can compare them against each other during a well-organised interviewing process, before choosing.

So what if there was a better way?

An alternative strategy

Fixing these limitations means that, rather than creating an elegant mathematical solution, we need to rely on brute force simulation. In return, the strategies coming out at the end are much more likely to tell us something useful in the real world.

Using the 37 per cent rule as a guide, we’ll keep the rules simple – “Interview candidates for the first X weeks, then as soon as you have a candidate available who is at least as good as the Nth best candidate you’ve seen already, hire them.”

What do the results of this modelling look like? The two outcomes we’ll keep an eye on are quality (the probability of hiring someone in the top 10 per cent of performance) and time (the number of weeks taken on average to fill the role). We will ignore cases where the role never gets filled. 

As you would expect, when we look at the quality side of the equation, it pays to look for a long time and to be choosy. Picking the 2nd best candidate you’ve seen after 10 weeks gives you an 84 per cent chance of hitting a top 10 per cent candidate.

But interestingly, you cannot be too choosy (if you hold out for someone better than the best person you’ve seen after waiting 10 weeks, then the possibility of never finding the right person changes.)

How should you balance these two opposing drivers?

One answer would be to express them both in financial terms. Specifically, the cost of spending longer hiring (which will be related to the cost of the interviewer’s time, and the penalty for leaving a vacancy open) versus the value of hiring a candidate who is great rather than ok.

Applying this evaluation approach to the model gives an intuitive result. The more impactful or important a role is for your business, the longer you should spend hiring for it. 

However, it also suggests that for the longest searches, you might not get the best result by holding out for the single best candidate. You might need to accept #2 if you’ve left it too long to hire the best person you’ve seen.

How should we apply the lessons of this model to real-world hiring decisions?

Although we have added some realism to these calculations beyond the very abstract 37 per cent rule we started with, the real world is definitely messier. Candidates don’t arrive in a neat queue and wait a fixed time before they accept an alternative job.

As such, rather than try to extract exact strategies from the model, it’s better to think in terms of the more general lessons it highlights:

• You need a wide net – the optimal hiring approaches suggested by the model generally involve interviewing a much larger number of candidates than a typical recruitment process. If you interview four candidates, your probability of not having seen a top ten per cent candidate is 66 per cent. After ten, this chance has dropped, but only to 35 per cent. The best way to get a top ten per cent candidate will often be to outsource the first phase of interviewing to a recruiter. They can talk to tens or even hundreds of potential candidates to assess their fit, before narrowing it to a shortlist for you.
• Pace of interviewing matters – A drawn-out process will mean that you lose potential hires. Quickly, they are snapped up by competitors or lose enthusiasm due to the wait. All things being equal, it will be much better to interview five people over a week, than to interview the same number over a month.
• In long searches, you might not get your top pick – If you’ve spent months looking, the second-best person you’ve interviewed might be the right person to hire. On the other hand, if they’re still not the person you want to hire, you may need to revisit your search parameters. You might have to alter the necessary skills, experience, sourcing approach or salary.

Recruitment success rates: Next steps for your business

In summary, although the strategy for a perfect hire in the real world is no more solvable with a spreadsheet than the quest for perfect love, maths can provide a window into new ways of thinking about the process, challenge our intuitions and beliefs, and perhaps even improve the outcomes.

Get in touch if you are currently recruiting and need help finding the right talent. You can also browse our other industry insights.