Year	% of expense
1972	40
1973	37.5
1974	38.095238095238095
1975	34.40860215053764
1976	30.46875
1977	33.95061728395062
1990	18.324543343580487
1991	18.525179856115106
1992	17.135450421257293
1993	18.846045064579993
1994	19.229504963513246
1995	19.36650164859703
1996	19.152534309082338
1997	21.42923707753479
1998	24.15850795519795
1999	22.445540661540953
2000	22.406127596126964
2001	22.390856511372302
2002	22.667393450109756
2003	22.881166451226008
2004	21.09770771304634
2005	20.08905328845296
2006	19.654895754041792
2007	17.31904751114381
2008	17.519009128078412
2009	18.07627609053419
2010	17.541467180286624
2011	17.12716715094111
2012	17.78238567538945
2013	18.44569349812298
2014	18.89774102001108
2015	18.57611684001471
2016	20.400785921052076
2017	19.506406850055022
2018	19.64283410486228
2019	18.959822701248612
2020	16.722898127663186
2021	15.643048759350817