I can answer your question.
There are requirements that need to be met, medically and psychologically, in advance of occupying an isolated duration post or a northern post. It is not specific to just the member, but also the member's spouse as well. Prior to our last northern post, my wife and I both underwent that type of testing, and it continues today. It does create some staffing challenges. There are times where the suitability is not there for one reason or another, whether it's a medical issue that would have exorbitant medical costs for a family to go into a northern post and then require travel outside of that post for attention....
It's an extensive psychological testing process as well. There's a very lengthy questionnaire, and in most instances a face-to-face meeting with a psychologist to have further discussion on the suitability of an isolated remote posting.