Cleveland Indians biggest year-to-year improvement/decline
based on regular season win percentage:

                            Change in 
                              win %
Improvement: 1985 -> 1986      14.9   (37.0  ->  51.9)
Decline:     1913 -> 1914     -23.3   (56.6  ->  33.3)
Last Year:   2006 -> 2007      11.2   (48.1  ->  59.3)