In their popular study on the 10 C's of Employee Engagement, authors Gerard H. Seijts and Dan Crim in the Ivey Business Journal listed "Congratulate" near the top.
According to their study, "Surveys indicate that employees feel that they receive immediate feedback when their performance is poor, or below expectations, but that praise for strong performance is, unfortunately, less common. Exceptional leaders give recognition, and they do so a lot."