Year	% of expense
1972	6.666666666666667
1973	12.5
1974	9.523809523809524
1975	11.827956989247312
1976	8.59375
1977	14.814814814814813
1978	23.52941176470588
1979	28.870292887029287
1980	21.770091556459818
1981	24.0251572327044
1982	22.288915566226493
1983	27.286791723070973
1984	29.20312352996519
1985	30.618326297491926
1986	19.492214733906575
1987	16.12546087981067
1988	25.68627450980392
1989	18.18878855000852
1990	39.488206372037496
1991	26.721479958890033
1992	25.897602073882048
1993	27.359291034222682
1994	23.463283150351717
1995	19.188814245398657
1996	14.895310263097569
1997	11.747872142147116
1998	12.592762187188825
1999	13.043478260869565
2000	13.240585704880974
2001	12.16148851958847
2002	12.075310478940468
2003	12.191153340827377
2004	11.902494090017088
2005	10.846004027194239
2006	11.10295924713186
2007	10.145980215858943
2008	9.095567212802361
2009	7.229323150070825
2010	6.668707694028095
2011	6.477433848352892
2012	5.965924140398362
2013	5.756346329556372
2014	5.139637772910344
2015	4.951523002769507
2016	5.537761476347033
2017	5.606742339995672
2018	6.274917836648199
2019	6.23197007723828
2020	5.654178803378825
2021	6.085173900184844