Year	% of total
1971	37.75932164298285
1972	38.25536527825019
1973	30.07663673819478
1974	31.871162420122033
1975	29.759626156879037
1976	30.604730837894312
1977	30.71777300429491
1978	32.00761318906864
1979	28.150450081733673
1980	25.964000438041946
1981	24.454563045099814
1982	21.684017202654477
1983	17.801263760921263
1984	16.0525349139851
1985	14.336289251585471
1986	14.766040090243518
1987	15.466378852651685
1988	14.075744732392057
1989	14.09252165070815
1990	12.381088273372772
1991	11.624514858205014
1992	11.659095195847993
1993	11.171399050498753
1994	9.757431202729252
1995	9.31812527373124
1996	9.401663310052857
1997	8.897804691929098
1998	8.445475647859565
1999	7.5796413857963
2000	6.51048910810205
2001	6.962158338660915
2002	6.511417783145795
2003	7.405839333414549
2004	6.99440950399458
2005	8.841994245392614
2006	8.546664149936523
2007	8.313924347298684
2008	4.8787791993137795
2009	4.894036952753077
2010	5.397245199713173
2011	5.338550550708393
2012	5.354163094041063
2013	5.632795030982291
2014	4.741989152463093
2015	4.368157386031051