Year	% of expense
1988	36.70664278482984
1989	38.20059958289885
1990	39.17001338688086
1991	38.91943715985675
1992	42.10845551069422
1993	38.929730028026
1994	43.579144595713984
1995	40.437520140364256
1996	42.47617890641739
1997	34.062731348471985
1998	40.81631844258215
1999	44.848823332133975
2000	44.81103641644705
2001	44.87776128865381
2002	44.032027218073
2003	50.892142941291475
2004	49.25321322317126
2005	45.92751858969975
2006	43.57041165931049
2007	40.226296864224935
2008	40.401548718145804
2009	48.75816048977472
2010	38.524830104402135
2011	34.47785223206033
2012	35.11211991431365
2013	30.682100127603746
2014	31.445153122307012
2015	29.366294778001112
2016	30.202849087007177
2017	26.75558739935556
2018	23.995126020704657
2019	24.15805921096689
2020	21.99282271672053