Year	% of total
1990	15.887102596614643
1991	17.006264176872612
1992	17.708609055974954
1993	18.304463906423365
1994	18.444733760892106
1995	18.578004741658326
1996	18.93909666884937
1997	19.293037092111145
1998	19.33209561705539
1999	19.44143743986409
2000	19.68491997620376
2001	20.347166696498604
2002	20.410024620152956
2003	20.36809807999209
2004	20.079956588132607
2005	19.84824200273771
2006	20.253314682283676
2007	20.32030800224016
2008	20.41358573945459