SN4 ""

No	Pattern	Freq
1	over a [adj] period [prep]	183
2	over a [adj] period [prep]	176
3	over a [adj] period [prep]	173
4	over a [adj] period of	143
5	over a long period [prep]	93
6	over a long period [prep]	85
7	over a [adj -er] period [prep]	10
8	over a prolonged period [prep]	9
9	over a prolonged period [prep]	9
10	over a short period [prep]	9
11	over a short period [prep]	8
12	over a longer period [prep]	8
13	over an [adj] period [prep]	7
14	over a [adj] period in	7
15	over a considerable period [prep]	7
16	over a considerable period [prep]	7
17	over a given period [prep]	6
18	over a given period [prep]	6
19	over a [adj] period to	5
20	over a [adj] period from	5