Year	% of revenue
1972	19.21206225680934
1973	19.561621174524397
1974	23.52517985611511
1975	24.164774570223805
1976	18.80122950819672
1977	19.081568462990145
1978	23.771912926218455
1979	23.480050664977835
1980	30.753809141940657
1981	24.190501888828926
2003	14.813448972955214
2004	16.903080986193373
2005	17.512979895763173
2006	19.867308018399154
2007	21.444576839172193
2008	20.209676702466083
2009	20.39438806885561
2010	20.185140017378313
2011	22.660485954404045
2012	21.6180121445126
2013	22.24804122874242
2014	21.512131090864077
2015	23.364927263605296
2020	19.507677603527235