The phrase "a difficult selection process" is correct and usable in written English.
It can be used when describing a challenging method of choosing or deciding among options, such as candidates for a job or participants for a program.
Example: "The company implemented a difficult selection process to ensure they hired the most qualified candidates."
Alternatives: "a challenging selection procedure" or "a tough selection method".
I had worked through a difficult selection process, I had made it to the beginning and I had no real idea what lay ahead.
Lee Yong Keun, chairman of South Korea's Financial Supervisory Commission, which has been overseeing the auction process for Daewoo Motor, said Ford "offered the best terms, and the Daewoo Restructuring Committee and creditors chose it as the exclusive negotiator after what I heard was a difficult selection process".
And Webster, who has taken over from Darren Edwards following his appointment as Newport Gwent Dragons head coach, said it was a difficult selection process.
It is also shaping up to be a particularly difficult selection process for the England manager when he has to weigh up whether Danny Welbeck and Daniel Sturridge can manage three tournament games in a week and the emergence of newcomers such as Dele Alli and Eric Dier means even the likes of Jordan Henderson and James Milner, two Hodgson stalwarts, may feel vulnerable.
Both, development and review process turned out to be time-consuming tasks, mostly due to difficult selection processes between alternative modelling approaches.
Once Karolyi, the national team coordinator, announced the Olympic team -- which included two members of the 1996 gold medal team, Amy Chow and Dominique Dawes -- he quickly discussed the difficult subjective selection process and exited the room.
The more difficult part is creating a selection process that identifies which ideas to implement.
Lawyers representing James Alex Fields Jr., 21, will face off against prosecutors in what's likely to be a difficult and tense jury selection process, given that emotions over that day in August 2017 are still so raw for many residents of the small Virginia college town.
Thus, these experiments reported on gene expression in dissected tissue, a method that would be difficult and costly to implement in a practical selection process.
It seems like a bollixed selection process".
