A study by the Journal of Happiness Studies has found that employee well-being and happiness accurately predicts employee performance. The researchers spent seven years studying over 900,000 soldiers and found that high-positive affect, low negative affect, and high optimism predicted awards for performance and heroism. However, the relationship between happiness and performance may be more than a correlation, rather than a causal relationship. The greatest degree of performance improvement occurs when an employee moves from "unhappy" to "fairly happy".