Kansas City Royals biggest year-to-year improvement/decline
based on regular season win percentage:

                            Change in 
                              win %
Improvement: 2002 -> 2003      12.9   (38.3  ->  51.2)
Decline:     2003 -> 2004     -15.4   (51.2  ->  35.8)
Last Year:   2006 -> 2007       4.3   (38.3  ->  42.6)