Table 2.3.

NOS score of included studies (case control)

Author	Selection	Comparability	Exposure	Total score
Hennessy, S.1996	4	2	2	8
Bista, M. B.2001	4	2	2	8
Ohrr, H.2005	4	2	2	8
Tandan, J. B.2007	4	2	2	8
Kumar, R.2009	4	2	2	8
Muangchana, C.2012	4	1	2	7
Florian Marks.2012	4	2	2	8