Table 1.

Example of search strategy used in our meta-analysis

S. no.	Database: Ovid MEDLINE(R) < 1946 to June Week 2 2012 >, Ovid MEDLINE(R) In-Process & Other Non-Indexed Citations < June 22, 2012 >, Ovid OLDMEDLINE(R) < 1946–1965>
Search strategy
1	Venous Thromboembolism/or thromboembolism/or venous thrombosis/or thrombophlebitis/(55500)
2	(Thromb$ and VTE).mp. or (venous$ adj3 thromb$).ti,ab. [mp = title, abstract, original title, nam0e of substance word, subject heading word, protocol supplementary concept, rare disease supplementary concept, unique identifier] (31130)
3	1 or 2 (67953)
4	Exp Neoplasms/(2369202)
5	Exp anticoagulants/or exp fibrinolytic agents/or exp platelet aggregation inhibitors/(284314)
6	(Prophyla$ or prevent$).ti,ab. (913626)
7	5 or 6 (1166445)
8	Cancer$.ti,ab. (932981)
9	4 or 8 (2540084)
10	3 and 7 and 9 (2759)
11	(Etiology or prevention & control or therapy or drug therapy).fs. (4835450)
12	10 and 11 (2431)
13	1 and 12 (2093)
14	(Cohort studies or case reports or Letter or Historical Article or comment).pt. (2672141)
15	13 not 14 (1702)
16	Exp Clinical Trial/or double-blind method/or (clinical trial$ or randomized controlled trial or multicenter study).pt. or exp Clinical Trials as Topic/or (randomi?ed adj7 trial$).mp. or (controlled adj3 trial$).mp. or (clinical adj2 trial$).mp. (992304)
17	15 and 16 (597)
18	th.xs. (5045165)
19	(Venous adj3 thromb$).ti,ab. (30982)
20	1 and 4 (5487)
21	18 and 19 (16219)
22	20 and 21 (1342)
23	22 not 14 (1083)
24	23 and 16 (383)
25	17 or 24 (666)
26	Remove duplicates from 23 (1060)
27	Remove duplicates from 25 (645)