Year	% of total
1971	18.21256521208936
1972	18.319075412882807
1973	18.527608348276807
1974	19.37075031879004
1975	18.90300202317931
1976	19.2023011980134
1977	19.149000744567925
1978	18.697229411980913
1979	18.888418919079896
1980	18.951898766345003
1981	19.22274545786808
1982	18.9393603399425
1983	18.603658985151455
1984	18.447333486716076
1985	18.055087407899833
1986	17.70163659665447
1987	16.992009083452615
1988	17.29921399560234
1989	16.941327900083767
1990	23.1570513875728
1991	23.16748332787487
1992	23.340263971054597
1993	24.410154135369112
1994	25.139087145169736
1995	25.067265495213427
1996	24.263423707612912
1997	23.89957521398033
1998	24.17225736686346
1999	23.34071486665853
2000	22.585200132707183
2001	22.232676153101323
2002	21.565306725975883
2003	20.517264966398795
2004	21.076432560531373
2005	21.008582635455124
2006	20.560489942168562
2007	19.754982255249775
2008	19.944408929843235
2009	19.863280312131327
2010	19.88897793897611
2011	18.797283261286022
2012	19.409545534420904
2013	19.1104525420208
2014	19.18975483686403
2015	18.997913170529536