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	31.515409315632283
2002	30.609518360613222
2003	33.685887339261384
2004	30.959055556661944
2005	28.535513580814712
2006	25.370591288186482
2007	24.13173033337638
2008	23.402988811287354
2009	28.749628402211606
2010	23.056055231143095
2011	20.456722334243988
2012	20.505743306324376
2013	17.93329262542151
2014	18.380307523131936
2015	17.67687157352764
2016	19.89172602251095
2017	16.90167618947347
2018	16.7179285852512
2019	16.869605174872973
2020	21.99282271672053