Year	% of total primary
1971	11.7095699310303
1972	11.5399198532104
1973	11.4432096481323
1974	11.3977899551392
1975	11.3546199798584
1999	15.0158700942993
2000	14.3578796386719
2001	14.3578796386719
2002	14.4341497421265
2003	14.2690496444702
2004	13.9573698043823
2005	14.1125602722168
2006	14.4530401229858
2007	15.4740800857544
2008	16.0340194702148
2009	17.0250301361084
2010	17.4281597137451
2011	17.5492992401123
2012	17.6639308929443
2013	17.8605098724365
2014	18.6789493560791
2015	19.2426891326904
2016	19.5592308044434
2017	19.1462001800537