Year	% of expense
1972	35.32823622462433
1973	39.00830483634582
1974	32.481816569097
1975	40.040682209357016
1976	41.09977324263052
1977	38.62102809471236
1978	39.66442186964949
1980	42.80754433705549
1981	41.054194506310246
1982	35.96732026143786
1983	38.49708659835248
1984	37.667240694131756
1985	39.03287185880192
1986	39.361836297136996
1987	40.574948665297676
1988	39.10690121786203
1989	37.495069033530534
1990	34.69478753288447
1991	33.384743148653534
1992	37.32704065215058
1993	40.01478576709203
1994	39.892159720198215
1995	37.34524067608232
1996	36.651327936537385
1997	34.71543586125131
1998	35.26318307459751
1999	33.69779281608707
2000	32.512420773810305
2001	34.740652770703754
2002	34.58273743546138
2003	31.684441664483998
2004	32.694506186542384
2005	31.851161110904176
2006	30.84016519515283
2007	30.573303778446466
2008	32.0109530079671
2009	31.96248965068009
2010	31.251406749920225
2011	30.836737243051697
2012	30.71333229976772
2013	30.698878214219494
2014	30.94240263837809
2015	30.873308065134232
2016	31.65898858965924
2017	31.73898617511525
2018	30.545249176189486
2019	30.81478220326032
2020	27.13315510723049
2021	27.73609821434035
2022	27.227697465881878