Don't think of information sources as "good" or "bad" - instead, consider whether they are appropriate for your research needs.
Wikipedia, for example, might not be appropriate for your research project on climate change, but if you're researching crowd-sourced reference sites, then Wikipedia will be an indispensable source of information for you.
Primary sources are firsthand or eyewitness accounts. They present the actual evidence of an event without any analysis or interpretation. Primary sources include diaries, letters, legal or court documents, laws, speeches, statistics, journals, original research documents, and the like.
Secondary sources analyze, interpret, retell, explain, or critique primary sources.
Tertiary sources index, organize, and compile other sources and are generally not referenced in academic research. This category includes encyclopedias, dictionaries, and textbooks.
Scholarly sources, such as journals, are written by the experts in the subject matter. They are often written for use by other scholars, researchers, or serious students of the subject. They often use language that is specific to that discipline. They usually include in-text citations or footnotes and a works cited or bibliography. They are often peer-reviewed, meaning the article has been anonymously reviewed by a panel of experts in the topic before it has been accepted for publication. They are usually published by a professional organization, research center, or scholarly press.
Popular sources, including magazines and news sources) are written for a more general audience, not necessarily experts in the topic. They are often written by journalists or others who are not professionals in the field. They are written in easy to understand language; they do not use technical jargon. Although they may have footnotes and/or citations, they are usually not as extensive. There may be little or no editorial review.
Professional/Trade sources are published for practitioners in specific fields. Generally, both the audience and the authors of trade publications are practitioners in the selected field.
Popular and trade publications are not better or worse than scholarly publications - each source must be judged individually and within the context of the information need.
Information sources are often classified as physical (print, analog) versus online (electronic, digital) text versus audio/video and book versus journal.
Here are some common information source types with descriptions of how current their information usually is, what kind of information is contained in them, and where to find them.
Gray literature is a huge category that encompasses a wide variety of documents that have not been published in the traditional sense. Gray literature includes:
Certain kinds of gray literature can be found in databases. Others are best found by searching the web.
Sometimes it is difficult to ascertain the author or organization responsible for the information, which can make gray literature may be difficult to cite.
What about video? What about the Web? Neither is a source type; video is a format, and the Web is a delivery method. You can find a video format textbook. You can find a scholarly article on the web. It does not necessarily change what kind of information is contained in it, who is responsible for that information, what kind of quality control is behind it, or how current that information is.
Material on this page is adapted from the Research Skills Tutorial by the Librarians at Empire State College has been made available under a Creative Commons Attribution-ShareAlike 4.0 International License.