Ad-driven skills gap? In a Business Insider piece I read that:

Michael Madowitz, an economist at the Center for American Progress, says he is &quot;unusually unsympathetic to the evergreen skills gap critique.&quot;
&quot;First the Econ 101 'pay more for more if you want more' cuts against this well in a period of little wage growth,&quot; Madowitz said. &quot;Second, there's fascinating/depressing empirical research showing a 'skills gap' occurs because employers add and remove qualifications for the same job postings depending on the labor market, ensuring there is always a skills gap.&quot;

(Emphasis mine.)
Unfortunately, the article has no further details on the latter research/issue to back up this statement that at least some of this &quot;skill gap&quot; is just employer advertisements vagaries, presumably regardless of what the job actually requires. And I'm curious if this is remotely quantifiable, i.e. how much of the &quot;skills gap&quot; in some sector (under study) turned out to be of this ad-based kind.
I don't buy the explanation of this being vagaries of advertisements, regardless of the job.

Instead, I see it as employers showing rational and predictable flexibility in response to a changing supply of labour. 

At times of plentiful supply, they can reduce recruitment costs by being far more selective at the first stage - filtering by essential requirements in the job ad. Finding good staff can be an onerous process. All the filtering stages after writing the ad are labour-intensive, and the labour is often line-managers and upwards, so not cheap. If I know I can get a decent number of interview candidates even with very stringent essential requirements, I'll do that, and that will reduce the number of applications that I have to process. This reduces my costs without significantly impairing the outcome.

At times of restricted supply, it's more cost-effective to advertise for lower essential requirements. That way, you cast a wider net, get more applicants, and are more likely to find a suitable candidate, without overwhelming the staff who have to read through the applications and process them.

As an occasional recruiter, I've done all this myself.