Year	% of revenue
1990	22.244761386925425
1991	19.095219280916634
1992	17.527373918654597
1993	20.676574284821708
1994	23.9423825590449
1995	25.77999776344727
1998	21.760155860421428
1999	26.628317155834274
2012	29.907531472211936
2013	32.562679777001
2014	33.51344095043125
2015	34.56535693773438
2016	38.632605541119695
2017	41.090226759533124
2018	42.67229467988313
2019	41.81666925739885
2020	42.287997866482776
2021	43.29183038226688