I am often told that as a leader, I must be encouraging to those around me. It then seems like a difficult balance between being reinforcing, but not too positive so that it looses its impact while still having the ability to correct course when headed in the wrong direction. Apparently this ratio of positive reinforcement to negative reinforcement has been studied and the magic number is 2.9013 (see link below). If positive to negative comment ratio is larger than 2.9013, then the person is uplifted, encouraged to new heights and their performance enhanced. If below the magic number of 2.9013, the person is deflated and performance suppressed.
Malcolm Gladwell discussed this phenomenon in Outliers, suggesting that children perform better in school when coming from a more positive home. Research suggest that more positive ratios are present in healthy marriages while low positive to negative ratios are present in struggling or divorce resulting marriages.
I have seen this principle work very well with my children. The single best piece of parenting advice I ever received was from a trusted mentor, Dr. Lew Sterrett. He suggested that the best way to encourage a certain behavior was to catch them doing something right. As I reinforce behavior with character traits and specific words like patient, kind, and obedient, the behavior truly changes. I have actually found that positive over negative reinforcement has been particularly successful in training my son to fall asleep and sleep through the night. The nights where I return after just a few minutes to praise him for resting quietly, lead to him falling asleep quickly. If I wait until he calls for me, having been gone long enough that it feels long to him, starts a cycle of repeated visits and increasing frustration on both sides.
Where I think it is most effective is after a corrective word or punishment. In instances where I must correct a behavior it is most effective to communicate my expectations when I praise for the exact opposite behavior once it is exhibited. For example, if my son is bothering his sister in the back seat of the car, I correct it, then follow up with words of affirmation about how I like him being sweet to his sister, it shows in his face how proud he is to receive praise. Now that I reflect on it, I usually follow up 2 to 3 times and based on the magic number it should probably be more consistently 3. Even days later I can come back to this topic, catching him being sweet to his sister when riding in the car and see the same pride in his.
I wish I could say that I am just as consistent in the workplace with this praise. As I have seen results in my own home, I know it works. Somehow it feels different praising adults, but the principles remain. We are still human and need reinforcement in much the same way, even if we have matured, at least a little bit.

http://en.wikipedia.org/wiki/Positivity/negativity_ratio