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Systematic reviews: Database years of coverage

PRISMA says to include database years of coverage - but it's not that simple

Why do we want to know the years of coverage?

It is helpful to know which publication years have been searched, particularly in the context of systematic reviews. This is an indication of the completeness of a search.

The 2020 PRISMA Statement advises researchers to include the years of coverage of databases searched, where provided. It suggests including a table of database coverage.

We suggest you don't copy the dates of coverage from the sample table in PRISMA 2020, as some of the dates are incorrect or may refer to something else.

Do database names reflect the years of coverage?

It is a common misunderstanding that names of databases that include dates reflect their years of coverage, but this is rarely the case. Older content is often added retrospectively and pre-print publications are often added in advance. This means years of coverage are fluid - constantly changing.

For example, in the database Ovid MEDLINE(R) ALL 1946 to July 27, 2022:

  • 1946 refers to the year that the Medline index started - before electronic databases existed.
  • In 1946, and now, they indexed past publications.
  • The earliest publications indexed in the database go back to the late 1700s - and this is fluid as older publications can be added many years later.
  • In this case July 27, 2022 refers to the latest update of the database searched.
  • Even then, the July 2022 update is likely to include pre print or non indexed publications with future dates.

Ovid Medline database guide - what is meant by "years of coverage"?

"But the official Medline Database Guide shows coverage from 1946!"

Unfortunately publisher sites can sometimes be confusing, and in the case of the Medline 2022 Database Guide this probably relates to their definition of "Years of coverage". Rather than the publication years of CONTENT, these "years of coverage" seem to refer to versions of the database or catalogue, which HOLD the content, or perhaps the date a record was indexed. Just be aware that these are quite different things to publication dates.

Proof that Medline covers more than just 1946 to current

Need some proof about date ranges?

Try a little experiment in Ovid Medline ALL which is often described as covering 1946 to the present.

Method 1: Scroll the drop down year limits to find the oldest year you can limit to eg 1860. 

Method 2: Search using the Year of Publication field (.yr) to find the oldest year where you get results eg 17*.yr. will retrieve records from the 1700s (over 600 results in Medline). 

The oldest publication will probably be on the last page like this:

Key databases - years of coverage

Years of coverage are constantly changing in most databases, and old publications are often added retrospectively. This is the best indication of coverage that we have been able to research, as at 29 July 2022. We checked official database guides and also ran tests in each database, including checking provided year limits. Please note that there appears to be no definitive answer.

Ovid MEDLINE(R) ALL 1946 to present

  • Indexed (catalogued) retrospectively from 1946 to present.
  • Early publications date back to 1781 while new records include pre-prints yet to be published.
  • Both older and newer records continue to be added.
  • The range of publication dates is fluid and does not indicate complete journal coverage.
  • Note: Years of coverage listed in the official database guide (1946 to present) do not reflect much older dates of retrieved publications (1781), or year of publication limits in the database itself (1860 to present).

Embase 1974 to present (Ovid)

  • Indexed (catalogued) retrospectively from 1974 to present. Note: Indexing may be from 1947 if you have Embase Classic.
  • Early publications date back to 1883 while new records include pre-prints yet to be published.
  • Both older and newer records continue to be added.
  • The range of publication dates is fluid and does not indicate complete journal coverage.
  • Note: Years of coverage listed in the official database guide (1974 to present) do not reflect much older dates of retrieved publications (1883), or year of publication limits in the database itself (1883 to present).

Ovid Emcare 1995 to present

  • Indexed (catalogued) retrospectively from 1995 to present.
  • Early records date back to 1917 and new records continue to be added
  • The range of publication dates is fluid and does not indicate complete journal coverage.
  • Note: Years of coverage listed in the official database guide (1995 to present) do not reflect much older dates of retrieved records (1917), or year of publication limits in the database itself (1917 to present).

Ovid Nursing Database 1946 to present

  • Indexed (catalogued) retrospectively from 1946 to present.
  • Early records date back to 1908 and new records continue to be added
  • The range of publication dates is fluid and does not indicate complete journal coverage.
  • Note: Based on year of publication limits in the database itself (1908 to present). Official years of coverage not located.

APA PsycINFO (Ovid)

  • Indexed (catalogued) retrospectively from 1806 to present.
  • Early records date back to 1707 and new records continue to be added
    The range of publication dates is fluid and does not indicate complete journal coverage.
    Note: Years of coverage listed in the official database guide (1806 to present) do not reflect much older dates of retrieved records (1707), or year of publication limits in the database itself (1860 to present)

CINAHL (EBSCOhost)

  • Years of coverage not provided.
  • Note: Earliest indexing for Year of Publication field is 1954.

Cochrane Library

  • Not defined.
  • Many records are sourced from Medline and Embase, so dates are likely to reflect those database coverages.

 

So what do we record?

If coverage constantly changes, how do we accurately record what we searched?

For many bibliographic databases it is not possible to accurately define the years of coverage. That is why we keep these records for systematic reviews:

  • the full name of the database on the day you searched it eg Ovid MEDLINE(R) ALL 1946 to July 27, 2022 (copy and paste this from the database when you are searching it - in Ovid it sits above the search box)
  • the full search strategy, including any limits
  • the date you carried out the search
  • the number of results you retrieved on that day

Table of database years of coverage

If you need to add a table of database of years of coverage (as per PRISMA 2020)

"If bibliographic databases were searched, specify for each database its name (such as MEDLINE, CINAHL), the interface or platform through which the database was searched (such as Ovid, EBSCOhost), and the dates of coverage (where this information is provided).

From Page M J, Moher D, Bossuyt P M, Boutron I, Hoffmann T C, Mulrow C D et al. PRISMA 2020 explanation and elaboration: updated guidance and exemplars for reporting systematic reviews BMJ 2021; 372 :n160 doi:10.1136/bmj.n160

There are a few options around how to respond to this requirement from PRISMA 2020. One is to decide whether the dates of coverage have actually been provided. If not, then you can simply provide the complete name of the databases eg Ovid MEDLINE(R) ALL 1946 to July 27, 2022. If the database name doesn't include the platform then just add it in brackets at the end eg Embase 1974 to 2022 July 27 (Ovid). Both of these show exactly what you searched.

If you want to create a table more like the example provided in PRISMA 2020, and try to explain years of coverage, then it might look something like this:

Full name of database Platform Years of coverage
Ovid MEDLINE(R) ALL 1946 to July 27, 2022 Ovid Indexed retrospectively from 1946 to present, including pre-prints, with publications dating back to 1781. The range of publication dates is fluid and does not indicate complete journal coverage for all years.
Embase 1974 to 2022 July 27 Ovid Indexed retrospectively from 1974 to present, including pre-prints, with publications dating back to 1883. The range of publication dates is fluid and does not indicate complete journal coverage for all years.

Or, if you want to include more data at the same time, all of which relates to dates, you might do something like this:

Full name of database Platform Years of coverage in database Date limits applied in search, if any Date searched Number of results Date range of retrieved publications*
Ovid MEDLINE(R) ALL 1946 to July 27, 2022 Ovid Indexed retrospectively from 1946 to present, including pre-prints, with publications dating back to 1781. The range of publication dates is fluid and does not indicate complete journal coverage for all years. No date limits applied 29 July 2022 457 1976 - 2023
Embase 1974 to 2022 July 27 Ovid Indexed retrospectively from 1974 to present, including pre-prints, with publications dating back to 1883. The range of publication dates is fluid and does not indicate complete journal coverage for all years. No date limits applied 29 July 2022 650 1971 - 2022

*This is not a PRISMA requirement, but could be interesting if you can easily work out the date range from records exported to EndNote before deduping. 

Guide Author

Helen Wilding, Senior Research Librarian

Carl de Gruchy Library, St Vincent's Hospital Melbourne
Helen.Wilding@svha.org.au

Literature Searching, Systematic Reviews, Mental Health liaison 
Thursdays, Fridays & alternate Wednesdays
Helen's profile | Researchgate | Orcid