| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | over a period of [noun pl] | 110 |
|
| 2 | over a period [prep] [noun pl] | 110 |
|
| 3 | over a period [prep] years | 62 |
|
| 4 | over a period [prep] weeks | 19 |
|
| 5 | over a period [prep] months | 17 |
|
