Sometimes it is relevant to supplement database searches with other search methods, such as reference searching, citation searching, the snowball method, manual searching, searching online, and contacting experts. Dependent upon the requirements of your literature study, your search strategy can encompass more search methods than just searching in databases, to avoid biases.

Grey literature— that is, scientific material that does not quite fit with the more common types of sources published by publishers, can sometimes be important to include in a literature study. What counts as grey literature can vary between disciplines. It can for instance refer to dissertations, public reports, conference proceedings, policies and guidelines, technical reports, unpublished data/studies/manuscripts, preprints, and ongoing studies etc. carried out by authorities, universities, and other organizations. Some of the grey literature, for instance dissertations, can be accessible in a database. However, it is often necessary to use other, more specific, freely available resources.

Remember! A search for grey literature must usually be adapted and simplified. It is often not possible to perform advanced searches in the various available resources for grey literature. If you would like support, contact the library!

Searching in citations and references

Citation search: When you search for citations, you find newer articles that refer to the original article. In addition, you may find more articles by going through the reference lists. In this way, you can progress in your search based on one more relevant studies or authors. You can use these search methods on the literature that is to be included in your literature study.

Use the following databases and search services for citation search (look for “cited by” or “citations” buttons).

Hand search

Hand search entails manually searching through a material, page by page. This can be useful in discovering new material that is not included in a database or in regular search sources, or if a source has been poorly indexed. An easier way to manually search is to only read through the contents of a journal or a conference within a certain period of time.

Ask experts

Contact people who are knowledgeable in the field.

Grey literature: Examples of sources

Using Google or Google Scholar can be a good start in the hunt for grey literature. It can be smart to search in the websites and archives of organizations. There are other resources and search sources that may be relevant. Below are some examples:

Databases for research published at Norwegian Universities, Colleges, and research institutes:

NVA (Nasjonalt vitenarkiv), Duo (The University of Oslo’s open archive), Norwegian Institutional Archives on Open Science, Cristin, Norart (Norwegian and Nordic Journal Articles), Oria

Note: The content from Cristin and Duo will transfer to NVA. For a short while, you will have to use all three systems.

General resources

BASE: Bielefeld Academic Search Engine
An international search service for gray literature.

Opengrey (1980-2020)
The System for Information on Grey Literature in Europe used to give open access to 700.000 bibliographical references of grey literature.

OAlster
Aggregated searches in over 2000 open sources. Operated by OCLC.

OSF- preprints
An open archive of preprints.

Dissertations

Proquest Dissertations & Theses Citation Index
You can access this database through Web of Science. From the pulldown menu under “Search in: Web of Science Core Collection”, you can select this database.

DART-Europe
A search service with open access to European dissertations from 580 universities in 29 countries.