It depends. Some of these techniques can definitely help if a person has enough clarity of mind to appreciate the technique and use it. So the clarity of mind is important. Now, we have a lot of students who have gone through depression in their life. They have used these techniques, it has helped them to relieve their depression. But with a long-term clinical depression it really depends. How long is this depression? How eager is the person to get out of the depression?
We've had people who have come to the retreats and they are on medication for different mental problems. Usually, they do quite well. The fact that they wanted to learn something to help themselves, that's the key, they actually wanted to learn something that could work better than the medication they were taking. So the key is really do they want to come out?
One of the problems with long-term clinically depressed people is that they are identified with their condition as themselves or ego, "I am this way, I cannot change, I have this disease, I will never be better, I am this!", and they freeze themselves. And if they freeze themselves, there is no way any of these technique can help because they don't want to change.
Even average people, if they don't want to change, then they can't change. If you don't want to or change, you won't develop in this practice.
The fact is all of you have had the good fortune to have heard the Dhamma and have changed from this practice. And, you want to continue to change.
The key is if they want it. The minute they want to change, yes, these techniques can start working. They have to apply them, while at the same time being realistic in how much they can do. So if a person is extremely depressed, a ten day retreat is not usually appropriate. A softer practice, something less intensive is more suitable and can definitely help.