0 (junk) | 8.6% |
0.5 | 9.9% |
1 (average) | 16.2% |
1.5 | 15.2% |
2 (good) | 22.2% |
2.5 | 12.7% |
3 (excellent) | 12.6% |
3.5 | 1.7% |
4 (superior) | 0.9% |
1910s | 0.03% |
1920s | 0.09% |
1930s | 0.31% |
1940s | 0.81% |
1950s | 1.21% |
1960s | 1.9% |
1970s | 4.3% |
1980s | 4.27% |
1990s | 16.92% |
2000s | 38.01% |
2010s | 27.07% |
2020s | 5.08% |