## Secondary sources

Sometimes you come across another interesting source in a source that you want to use for your paper. For example, a certain book may be cited in an article you are reading. In this case, the book is considered the original (primary) source, and the article in which the book is cited is the secondary source.

Avoid citing secondary sources as much as possible. In principle, only works that you have read yourself should appear in the reference list. If you are unable to access the original work—for example, if it is an out-of-print book, an old print-only report, or a work available only in a language you do not read—you may cite the secondary source.

Suppose a work by Smith is cited in Jones, and you have not read Smith. In the text, mention the primary source (Smith) and then include a reference to the secondary source (Jones). Use the phrase “cited in.”

Example in APA style:

A previous study (Smith, 2009, cited in Jones, 2020) found no significant differences between the two age groups.

- Example Vancouver style:

An earlier study by Smith, as cited in Jones (1), found no significant differences between the two age groups.

In the reference list you only list the details of the secondary source.