Year	% of expense
1978	26.29629629629627
1979	26.130653266331592
1980	25.64899045928558
1981	23.892133287530065
1982	24.62083628632174
1983	21.482358003442354
1984	22.74437815511707
1985	19.841423322374812
1986	19.155261674099105
1987	20.95523578985545
1988	22.459595190486993
1989	28.80837034046561
1990	28.97356014446809
1991	29.708122110810898
1992	30.516540026095658
1993	30.09244613167426
1994	30.254017625712788
1995	29.72758435063766
1996	30.03640833850466
1997	30.95655324068463
1998	30.75804492028036
1999	31.29136082276088
2000	32.280200105305376
2001	31.680366792155006
2002	31.901672936103974
2003	31.231267644938903
2004	30.621671252975112
2005	30.38554394064069
2006	29.092911596592852
2007	28.068793681842408
2008	27.244478763674294
2009	26.670577745089307
2010	24.8517098626705
2011	22.935371102335232
2012	20.791668895909446
2013	21.683902086447926
2014	19.754330679100534
2015	20.42044710932906
2016	21.61094168611129
2017	20.910424934006013
2018	21.6997767496692
2019	22.057728334835137
2020	21.003627387629297
2021	21.3217366419603
2022	20.814216640009548