Year	% of total
1971	23.588959523875154
1972	22.176722958654988
1973	18.575543299005346
1974	21.63052592756502
1975	21.09520926751517
1976	19.703975809910673
1977	17.248758977931285
1978	15.79334910344698
1979	16.723072508465503
1980	17.336917146970702
1981	18.000353352505012
1982	17.611018505064806
1983	17.769859811610164
1984	16.116281693730876
1985	16.77135668194976
1986	16.560325000107493
1987	15.189905649689688
1988	15.674097045174676
1989	15.47671726383649
1990	14.609550548093624
1991	13.943467529549524
1992	12.983019169303574
1993	13.612228401937019
1994	12.310421968119908
1995	13.127861599340761
1996	12.254554483266038
1997	11.989651937870748
1998	12.326650566390922
1999	11.602887556970485
2000	11.503463115964573
2001	12.442533478139467
2002	11.798309385990793
2003	11.231396349667781
2004	11.828073984343476
2005	11.425321567274636
2006	11.597003611479002
2007	11.25011261816564
2008	12.613208599778433
2009	12.651503936501593
2010	12.91312625646964
2011	12.045330730931763
2012	13.804029804595636
2013	13.666465420198701
2014	14.95630513793298
2015	15.222083057081438