"Bejeweled 2 was found to reduce stress activity by 54% compared to the control group. Peggle and Bookworm Adventures did not reduce subjects' physical stress levels significantly but did affect psychological tension, depression and other aspects of mood, in some cases dramatically.

Peggle had the greatest affect, improving mood by 573% across all study subjects - with Bejeweled 2 at 435% and Bookworm Adventures at 303%."