Year	% of expense
1972	17.586206896551722
1973	33.64140480591497
1974	38.07106598984771
1975	35.99101628298709
1976	35.28988116672668
1977	38.5666347075743
1978	32.330708661417326
1979	32.807756341200665
1980	31.409533021656188
1981	32.263185747045334
1982	31.773796382779995
1983	30.67382450944095
1984	27.80195455435257
1985	28.301969365426693
1986	23.764735448381135
1987	22.588991546160667
1988	22.9835115358713
1989	22.26855713094245
1990	21.40159462861939
1991	18.95115486558122
1992	17.075171777253615
1993	15.491803278688524
1994	15.893965031020867
1995	16.511081667068176
1996	16.803008312442273
1997	16.122370166395218
1998	15.423667700295665
1999	17.61433954917748
2000	14.97388197105877
2001	23.627407172382444
2002	22.225911642374967
2003	20.899377479803572
2004	21.79797710324329
2005	22.335612725357525
2006	22.46705149100896
2007	22.673469348447213
2008	23.67473596450473
2009	24.604579475221716
2010	23.016561682978118
2011	23.62440296718227
2012	23.084634233598926
2013	23.05798663455827
2014	23.39569595718924
2015	22.980096981646167
2016	32.60547914173143
2017	25.745304272591962
2018	25.19306348505193
2019	25.823821589893726
2020	25.025940762537992