0 (junk) | 8.4% |
0.5 | 10% |
1 (average) | 16.4% |
1.5 | 15.2% |
2 (good) | 22.3% |
2.5 | 12.8% |
3 (excellent) | 12.5% |
3.5 | 1.6% |
4 (superior) | 0.9% |
1910s | 0.03% |
1920s | 0.1% |
1930s | 0.32% |
1940s | 0.77% |
1950s | 1.22% |
1960s | 1.96% |
1970s | 4.31% |
1980s | 4.12% |
1990s | 17.34% |
2000s | 38.85% |
2010s | 26.92% |
2020s | 4.05% |