Year	% of expense
1973	3.032345013477085
1974	2.3584393000760833
1975	2.439848677816293
1976	3.1434774210978373
1977	3.052567792758675
1978	3.783033054135354
1979	4.011400650987161
1980	4.402914495667165
1981	4.581746073161823
1982	4.526641485172383
1983	5.9065844249253585
1984	6.9549104385423
1985	8.359906920623953
1986	9.579175399784543
1987	8.929763477888947
1988	9.045610687175136
1989	9.102125934134236
1990	9.46361789470114
1991	8.881825649083984
1992	9.021868113239567
1993	8.871946600467172
1994	9.259436215957935
1995	6.939770765591649
1996	7.55993377247518
1997	7.592787881207072
1998	7.462856934674618
1999	7.213367540189706
2000	7.5079701019353395
2001	6.664361174016355
2002	6.042775335758711
2003	5.7582656664441
2004	5.577125032052994
2005	4.8500946549558
2006	4.498326816939162
2007	4.455545960135542
2008	4.622023233838085
2009	4.73477346220281
2010	4.614796355629392
2011	5.3422306223602245
2012	5.867861282130489
2013	5.498951312800713
2014	5.931684942891541
2015	5.752184372326516
2016	5.297354886065497
2017	4.718042357688589
2018	4.178624120540293
2019	3.820513360961238
2020	3.1061529966268715
2021	2.7808197644456563
2022	2.9202030409152