"Employment at graduation" is not a particularly meaningful metric, because STEM PhDs who are not employed at graduation usually just means that they haven't gotten a post-doc. They will take a few months and find a job in the tech industry.
In addition : The end-date of a PhD is indeterminate (at least in the UK), since one doesn't know for sure whether the thesis defense will require any re-writing, etc. So it's difficult to have a job fixed up completely on the day the magic letter arrives.
I chose to travel around Europe for a few months after school and then bothered looking for a job, so I guess by this metric I was unemployed.
In the end I left Kansas for a job in London, a much better choice for me than being employed at graduation.
