1960s
6.8
7.5
7.9
7.4
6.6
6.9
7.7
7.7
0.0
5.5
8.4
7.2
6.0
8.4
7.2
7.8
8.8
7.4
7.4
7.3
7.6
8.1
7.1
7.5
7.5
7.7
7.8
7.2
8.0
6.5
7.1
7.2
7.7
7.5
6.0
7.6
8.1
6.9
7.4
7.0
7.1
7.0
7.3
7.5
6.8
8.0
7.5
7.7
7.1
7.5
7.7
7.6
6.6
7.0
6.7
7.6
7.9
6.7
7.9
7.3
7.1
0.0
6.2
6.6
6.7
7.8
7.2
7.3
6.3
6.9
7.1
7.3
7.7
7.2
6.7
7.5
7.1
7.2
6.9
5.8
7.7
6.3
6.9
6.5
0.0
7.1
7.8
7.0
7.5
3.0
6.8
7.6
7.1
8.0
6.5
6.7
6.3
6.9
7.3
6.2
7.0
0.0
6.5
7.2
7.8
7.2
6.0
6.4
5.7
7.0
7.1
7.7
6.8
6.5
6.7
6.9
8.2
8.2
6.7
6.6
