Table 1 Advantages and disadvantages of using bibliographic databases and web-based search engines

Advantages

Citations are entered into individual databases according to selected journals so all entries are legitimate academic sources

Duplicates are uncommon [0.01% ± 0.0 (SD) (n = 10,000 records) (Haddaway et al. in press)]

Citations are classified according to predetermined subject categories

Full citation information is typically provided; including full abstracts (where available), author contact information and keywords

Some grey literature may be included (such as conference proceedings and theses)

Citations are identified automatically according to multiple criteria, including; the presence of a bibliography, a title followed by authorship (see http://scholar.google.co.uk/intl/en/scholar/inclusion.html for details)

Citations are collated on approximately a weekly basis so they are very up-to-date

All citations are included, not just those from specific journals or publishers

A wide range of grey literature is also included (such as organisational/government reports)

Access to the search facility is free-of-charge

Introduction of typographical mistakes in catalogued citations is avoided since citations are taken directly from their sources

Articles published on multiple sites are combined into single entries to minimise duplication

Disadvantages

Not all legitimate academic sources are included

Inclusion may take considerable time, sometimes several months or more since first appearing online

Typically cannot include ‘online first’ manuscripts that are published online but not in print

Subscription costs may be high

Typographical mistakes may be introduced as citations are transcribed manually (although many databases receive citations electronically)

Duplicates are relatively common [0.6% ± 0.6 (SD) (n = 6988 records) for full text searches and 3.1% ± 1.5 (SD) (n = 4194 records) (Haddaway et al. in press)] [duplicates are caused by errors during automatic text scanning and manual entry]

Mistakes at source are copied into collated citations, contributing to duplicate entries where citations are published on multiple sites

Citations are not full, since titles, abstracts and journal names are often shortened to fit into limited space

Citations may only be exported singly

Reproducibility of searches may be particularly low in comparison to bibliographic databases