Table 2.

Relationship between number and year of studies based on search methodology.

Year	Number of studies	%
1987	1	2.70
1991	1	2.70
1996	2	5.41
1997	1	2.70
1999	1	2.70
2000	1	2.70
2001	6	16.22
2002	7	18.92
2003	4	10.81
2004	2	5.41
2005	2	5.41
2006	3	8.11
2007	2	5.41
2008	4	10.81
	37	100%