Year	% of expense
1974	11.309867282169648
1975	11.163978182662179
1976	12.245107080643509
1977	12.26207906295754
1978	13.167427941408096
1979	12.421135646687699
1980	13.097036606624055
1981	14.057491732383617
1982	15.212218232163718
1983	16.36992348440259
1984	17.03424347563735
1985	17.329455185393396
1986	17.709335899903753
1987	18.75701065619742
1988	20.030014256771967
1989	20.97507108042242
1990	22.361724547676165
1991	24.56587651598677
1992	25.250725670484762
1993	25.996834250395718
1994	27.62580051846274
1995	27.440842183715297
1996	28.13900203665988
1997	27.1387659925346
1998	28.677950702184486
1999	29.514885694580812
2000	29.648082725577307
2001	29.271030426290363
2002	28.690851656178616
2003	27.61621023932838
2004	25.64459366698258
2005	23.382347070969523
2006	22.578359040380285
2007	22.202049419946455
2008	19.733883531938186
2009	19.37223868911135
2010	18.280664719700336
2011	18.196906499826206
2012	19.45783207474403
2013	19.487563599788135
2014	21.235596948906718
2015	20.714889555953146
2016	20.386044802025687
2017	19.833401912265437
2018	19.3965097896145