Table 1 Definitions and formulae for the search performance metrics used to evaluate the complementary approaches

Proportion of studies missed^b

Number of records not identified by the search, out of the total identified by the reference standard:

# relevant studies complementary search approach/# studies included using the reference standard approach × 100

Precision (specificity)

The number of relevant studies identified by the search, relative to the total number of records identified by the search:

# relevant studies identified/# records retrieved by the search × 100

Sensitivity

The number of records correctly identified by the search, relative to the total number of relevant studies that exist (identified by the reference standard):

# records retrieved by the search/total number of potentially eligible articles that may exist × 100

Number needed to read (NNR)

The number of records identified by the search that need to be screened to locate one included study:

1/precision