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Distribution of US schools amoung different periods of construction
| Period of construction | Age class | Proportion of schools surveyed (%) |
|---|---|---|
| 1901-1920 |
80 |
3 |
| 1921-1930 |
70 |
7 |
| 1931-1940 |
60 |
5 |
| 1941-1950 |
50 |
6 |
| 1951-1960 |
40 |
26 |
| 1961-1970 |
30 |
24 |
| 1971-1980 |
20 |
13 |
| 1981-1990 |
10 |
8 |
| 1991-2000 | 0 | 9 |
Data were from Lewis and others [76].
