Year	% of total
1990	17.785616768605564
1991	16.760343934944228
1992	15.89379165073026
1993	15.826052719491733
1994	15.6376438040748
1995	16.87383367348521
1996	17.439698946799798
1997	16.666375243857313
1998	17.23679971069918
1999	17.691383868842777
2000	18.224085826259294
2001	18.631084906396826
2002	18.76243317586561
2003	19.08259270783038
2004	18.98164771950327
2005	19.48452901350919
2006	18.923144705212522
2007	18.12447532723668
2008	18.154806969104776
2009	17.547124339989473
2010	18.36354355543156
2011	17.84375231954404
2012	18.151814690966148
2013	18.184441108058504
2014	17.406511606474496
2015	17.558208945157872
2016	17.97442532303199