Year	% of total
1971	36.224906195062005
1972	36.207558394234916
1973	37.48217249736117
1974	37.51338182166393
1975	37.69131322668514
1976	38.368493388259765
1977	38.61993559908896
1978	39.5247498983258
1979	39.51057033830003
1980	40.36105366858343
1981	41.94229472506849
1982	43.21243431225519
1983	42.873793062158164
1984	43.17578876134425
1985	42.578602568679294
1986	42.421521250687725
1987	43.10055040252015
1988	42.84432431484577
1989	41.28117452701425
1990	40.650918124794096
1991	41.1803746718142
1992	39.4239648860884
1993	40.26172865973305
1994	39.1467534373012
1995	39.651364501404544
1996	39.41852574056133
1997	39.45457900155032
1998	38.55118960079543
1999	38.89943230778959
2000	38.2363154370916
2001	38.897670946872694
2002	38.01463961722679
2003	39.08267870120901
2004	39.90807248901161
2005	39.626517937918855
2006	38.93769166036472
2007	39.61722475471026
2008	40.96648795156825
2009	39.856791040459356
2010	39.59751226282024
2011	39.17406749768438
2012	38.70217196102579
2013	38.27411641824491
2014	39.78936584348552