Year	% of total
1971	44.52551220460082
1972	42.85054794182416
1973	41.53432716427518
1974	38.5712586910542
1975	38.293914437511134
1976	36.81956615096976
1977	36.69204844437772
1978	37.2905709196715
1979	36.42818239900178
1980	36.115978583291806
1981	34.846549744650815
1982	34.803664622833345
1983	34.0301173269555
1984	31.929693584526913
1985	30.296348567139525
1986	31.994211308446808
1987	31.37083814719303
1988	32.08769222008002
1989	32.28577113420699
1990	29.963339786974014
1991	30.100646357551835
1992	30.243211096737255
1993	28.920833013495084
1994	30.15417994555909
1995	29.76722541222089
1996	30.194384060608925
1997	30.933176733239577
1998	33.65397986313795
1999	34.556916127584245
2000	34.85540057546678
2001	37.226664525355545
2002	36.81623510036166
2003	37.93740799220437
2004	38.051821308662085
2005	37.35255843858409
2006	36.70912092885321
2007	37.60479604468632
2008	38.58793887776451
2009	37.998129685627354
2010	39.39446574786039
2011	38.22971433832163
2012	41.07154976770497
2013	42.73814326446775
2014	43.06019806095685
2015	44.37835297581481