1960s
7.3
6.8
6.9
5.6
6.7
6.6
7.7
7.0
7.2
7.4
6.5
6.0
5.9
5.6
6.4
6.4
6.4
7.3
7.3
7.5
7.2
7.0
6.8
0.0
7.7
6.1
6.2
7.3
0.0
7.2
7.9
7.1
7.4
6.5
7.1
6.3
7.2
6.3
7.9
6.6
7.2
6.2
7.7
6.3
7.1
6.3
6.1
7.9
6.5
7.5
6.2
6.9
7.4
6.3
6.7
6.5
6.9
6.9
7.5
6.5
7.1
6.0
7.1
6.8
6.4
6.8
6.1
4.7
6.0
6.5
6.5
6.1
6.4
6.5
7.1
7.4
6.7
6.6
7.7
5.5
7.1
7.5
7.7
5.4
6.6
7.1
0.0
7.0
6.5
7.6
5.5
6.8
7.7
6.2
5.9
7.9
5.5
7.0
7.0
0.0
6.7
8.0
5.3
6.5
7.6
8.1
7.6
6.9
6.4
0.0
0.0
4.8
7.2
7.1
7.0
6.3
7.2
7.0
6.4
6.8
