Documentary sources of information can be categorized based on the originality and organization of their content into three types: primary, secondary, and tertiary. This categorization generally applies to scientific and technical literature and helps in understanding how information is generated and disseminated.
Primary Sources
Definition: A primary source is a document that contains newly generated information, original research, or a new interpretation of known facts. It is the first, and often the only, published record of an original work. Information in primary sources is generally scattered and unorganized, as it is newly reported and has not yet been fully assimilated into the established body of knowledge. These sources are the foundational materials upon which a subject is built.
Examples of Primary Sources:
The sources provide numerous examples of primary documents, which can be both published and unpublished:
- Research Periodicals (Primary Periodicals): These are journals that are wholly or mostly devoted to publishing original research papers, which are typically peer-reviewed. This category includes "letters journals" which publish short communications for rapid dissemination.
- Technical Reports: These reports originate from mission-oriented research projects, often from government or industrial organizations, and detail the scope, methodology, and results of the research.
- Conference Documents: Documents generated from conferences, such as the papers presented, often contain nascent ideas and original contributions.
- Patents and Standards: A patent is a primary source that provides the first detailed description of an invention. Standards are also considered primary sources that establish rules for measure, quality, or performance.
- Theses and Dissertations: These are documents that contain the detailed results of research conducted for an academic degree and are considered original works.
- Official Publications: Governments generate both primary and secondary documents. A journal like the Defence Science Journal is an example of a primary government publication.
- Trade Literature: This includes manufacturers' catalogues, information leaflets, and user guides that provide primary, application-oriented information about products and processes, much of which is not published elsewhere.
- Unpublished Sources: A wide range of unpublished materials are considered primary sources, including laboratory notebooks, diaries, personal correspondence, memoranda, internal research reports, official files, and medical records.
- Audio and Video Tapes: Recordings of lectures, discussions, experiments, or surgical operations are also primary sources.
Secondary Sources
Definition: A secondary source is one that is more or less completely dependent on primary sources for its existence. These sources gather information from primary documents and then compile, organize, and arrange it according to a definite plan. By organizing scattered information, they overcome barriers like language and provide a coherent overview of a topic. They serve as a key to accessing primary sources.
Examples of Secondary Sources:
- Secondary Periodicals: These are journals that organize and present information from primary sources. They include:
- Indexing Periodicals: Such as Index Medicus, which systematically lists articles from primary journals.
- Abstracting Periodicals: Such as Chemical Abstracts, which provide abstracts in addition to bibliographic details.
- Reviews of Progress: Serials like the Annual Review of Immunology that consolidate, evaluate, and summarize the literature on a topic for a specific period.
- Popular Periodicals: Magazines like Science Reporter that interpret advances reported in primary sources in a lucid style for a general audience.
- Reference Books: A large category of secondary sources that draw material from primary sources. Examples include:
- Encyclopedias, Dictionaries, Handbooks, Manuals, Yearbooks, Directories, Gazetteers, Atlases, and Biographical Sources.
- Bibliographies: A bibliography is a list of documents. If it lists primary sources, it is considered a secondary source.
- Treatises and Textbooks: A treatise is a long, serious work on a particular subject. A textbook is a standard work used for study. Both are generally considered secondary sources as they are based on primary information, though some authors may place them differently.
- Translations: A primary source translated into another language becomes a secondary source.
- Bibliographic Databases: Machine-readable databases like MEDLINE or CAPlus that contain records from indexing and abstracting services are secondary sources.
Tertiary Sources
Definition: A tertiary source is one that is entirely dependent on secondary sources, or on a combination of primary and secondary sources, for its existence. These sources act as a key to both primary and secondary sources, helping a user to find them.
Examples of Tertiary Sources:
- Bibliography of Bibliographies: This is a list of bibliographies. Since a bibliography is a secondary source, a list of them is a tertiary source. An example is the Bibliographic Index.
- Guides to the Literature / Guides to Reference Sources: These guides help a researcher find primary, secondary, and tertiary sources on a specific subject. Examples include Walford's Guide to Reference Material.
- Directory of Directories: This is a list of available directories.
- Library Catalogues: Library catalogues, including union catalogues, are considered tertiary sources because they list documents that belong to primary, secondary, and tertiary categories, reflecting the entire collection of a library or group of libraries.
Lack of Unanimity in Categorization
The sources make it clear that there is no complete agreement among authors on how to categorize every type of document. The criteria for categorization are not yet firmly fixed, leading to some sources being placed in different categories by different experts.
- Textbooks: Some place textbooks under secondary sources because they contain facts originally reported in primary literature. Others place them under tertiary sources because they often reference other secondary sources like encyclopedias and other textbooks. One author even places them under primary sources, though this is an exception.
- Monographs: "Research monographs" that contain original research results are considered primary sources. However, other monographs that are written by culling information from primary sources are considered secondary.
- Directories and Lists of Research in Progress: These are sometimes considered tertiary sources by authors like Grogan. However, since they are often compiled from raw data gathered directly from people or institutions via questionnaires, they can also be seen as primary sources. Because they are used as reference tools, they are also frequently placed among secondary sources.