Table 4.

Frequency of misses on a per review basis, three strategies compared

	Number of reviews with items in MEDLINE, but missed
Number of items missed	HSSS123	HSSS12	NBSS
1	14	19	23
2	2	2	7
3	2	6	8
4	-	2	4
5	-	1	2
6	-	1	2
10	1*	1	-
12	-	-	1
16	-	1*	-
23	-	-	1*
N of reviews with missing items	19	33	48
Median missed items per review	0	0	0
Interquartile range	0 – 1	0 – 1	0 – 0

* These misses are attributable to review #129, Wilhelmus KR. Interventions for herpes simplex virus epithelial keratitis. Cochrane Database of Systematic Reviews 2002; The Cochrane Library, Issue 3, 2002. This review had 146 included studies, of which 89 could be found in MEDLINE. 73 of these were retrieved by the HSSS12, 66 by the NBSS. An additional 6 could have been retrieved by phase 3 of the HSSS, which the authors did not report using.