Table 3.

Characteristics of studies.

	N	(%)
Allocation
Non randomized	33	9
Randomized	318	84
Unspecified	26	7
Study design
Single group	36	10
Parallel	269	71
Factorial	4	1
Crossover	3	1
Other design	11	3
Not specified	54	14
Registration status
Prospective	205	54
Retrospective	129	34
Unspecified	43	11
Intervention purpose
Treatment	28	7
Prevention	297	79
Other	52	14