A secondary citation is created when an author is cited from within another author's work.
It is always preferable to read and cite the original work, and every effort should be made to obtain it. If the original source cannot be obtained, cite the original source, rather than the secondary source in the text of your paper, e.g., if Loftus has cited Hashimoto, but you have not seen the work by Hashimoto: Hashimoto et al1 reported that the statistical analysis suggested. In the reference list, include the work by Loftus after the work by Hashimoto and include the text ‘Cited by’:
- Hashimoto DA, Rosman G, Rus D, Meireles OR. Artificial Intelligence in Surgery: Promises and Perils. Ann Surg. 2018;268(1):70-76. doi:10.1097/SLA.0000000000002693. Cited by: Loftus TJ, Filiberto AC, Balch J, et al. Intelligent, Autonomous Machines in Surgery. J Surg Res. 2020;253:92-99. doi:10.1016/j.jss.2020.03.046