Year	% of revenue
1975	28.21316614420067
1976	27.23704866562011
1977	27.609427609427545
1978	27.966881324746883
1979	25.154264972776826
1980	25.75677110993091
1981	26.00972721505607
1982	25.533717383937592
1983	22.310756972111527
1984	22.318320852230844
1985	22.62533552688552
1986	24.687656171914085
1987	26.308586363410104
1988	25.952608883818563
1989	23.070993061882376
1990	24.166121648136052
1995	29.402417523280704
1996	28.386308414539524
1997	28.561506465225605
1998	29.380086539329103
1999	28.1913192667126
2000	29.27836286477942
2001	30.020782451498963
2002	29.82239608043739
2003	31.169399750747967
2004	31.240656204023775
2005	31.601760133057134
2006	30.533097111677442
2007	29.70985699055718
2008	30.467821503504748
2009	32.7885019964145
2010	32.470034801036995
2011	31.387621934870314
2012	29.414502779537504
2013	29.26972540153489
2014	29.282823568668633
2015	29.1156892703185
2016	29.692551831215848
2017	29.96257778890173
2018	29.790601966188067
2019	30.496500895999347
2020	32.343358111035414
2021	31.157332929646653
2022	30.619967336759835