Philadelphia Phillies biggest year-to-year improvement/decline
based on regular season win percentage:

                            Change in 
                              win %
Improvement: 1904 -> 1905      20.4   (34.2  ->  54.6)
Decline:     1993 -> 1994     -12.9   (59.9  ->  47.0)
Last Year:   2007 -> 2008       1.9   (54.9  ->  56.8)