No case studies here right now.
Just beginning to learn about this skill. Maybe read a book or attend a training session, you have an idea what it is about but you haven't had a chance to use it yet.
You have learnt this skill and have been able to put it into practice. You should be able to describe some situations where you have used it, and possibly have evidence of using it.
You use this skill almost every day, and have done for years.
Not only do you use this skill everyday but you are often called to guide others.
You are considered to be the expert when it comes to this skill, and lead the way when it comes to developing new techniques.