Year	% of total primary
1972	12.0645198822021
1973	14.2741298675537
1974	16.5205307006836
1975	16.1005897521973
1976	17.2297306060791
1977	17.145450592041
1981	19.5989208221436
1982	20.1326293945312
1983	20.2260894775391
1984	20.6871604919434
1985	21.0448303222656
1995	26.3334503173828
1997	29.7127304077148
2001	33.7971382141113
2002	35.1527481079102
2003	35.2326316833496
2004	35.3222503662109
2005	34.0756301879883
2006	35.4211196899414
2010	37.3351211547852
2011	37.0830497741699
2012	37.4525604248047
2013	37.336238861084
2014	36.7317085266113
2015	37.6657791137695