There is some interesting research on worker engagement as reported by HR Dive. There is a clear correlation between a drop in engagement and the time before an employee quits. Unsurprisingly, quality managers, challenging work, and rewards for performance all enhance retention.
Further emphasizing the importance of providing workplace engagement is a recent survey from CNBC around automation threatening worker jobs. Employers that help their workers stay relevant improve workplace satisfaction.
An interesting article from Thrive Global suggests that humor is an important tool for boosting productivity and workplace happiness but it must be deployed properly.