Year	% of expense
1991	16.67277870913663
1992	17.09902132569768
1993	17.3183159023867
1994	18.992523058451127
1995	23.29168842646527
1996	29.050615961435454
1997	29.18909421968088
1998	26.947321322823043
1999	25.831268902837518
2010	19.23282250387322
2011	18.67040736885227
2012	17.44966220636632
2013	18.573313520812395
2014	15.993473646294031
2015	15.287578133457263
2016	17.609997091744457
2017	16.505728597586128
2019	15.529729815005936
2020	17.36822805113912
2021	17.804720146709787