Q. When doing a systematic literature review, should I include in my references papers that have influenced my work but which aren't part of my dataset?

You might ask this about various types of sources, including:

• sources that have influenced your research methodology
• and papers that are relevant in some way to your research question, but which have not appeared in your literature search results or not met your systematic review inclusion/exclusion screening criteria. 

In a systematic review/systematic literature review, sources that have influenced your work can and should be included in the list of references, whether or not they are part of the final dataset of papers (following a comprehensive literature search, screening process and critical appraisal). If you do not reference sources that have influenced the research you are in danger of plagiarism.

It is normal and expected in a systematic review/systematic literature review to have references beyond your set of papers for analysis, e.g. this review Does chief executive compensation predict financial performance or inaccurate financial reporting in listed companies: A systematic review - Rousseau - 2023 - Campbell Systematic Reviews - Wiley Online Library lists in Table 3 the 25 papers in its final dataset, but there are many more than 25 papers in the list of references. Similarly, this paper Religious identity in the workplace: A systematic review, research agenda, and practical implications - Héliot - 2020 - Human Resource Management - Wiley Online Library lists 52 papers in table 2, but has lots more references listed at the end. (I’ve selected papers that seem to me to be good quality reviews – I know there are lots of published systematic reviews that have areas for improvement!)

If a source in your set of papers following screening refers to another paper but you don’t have access to the original paper, it is appropriate to do secondary referencing, including both sources in your citation but only the paper you have read in your list of references. It is ideal to look at the earlier work yourself and to include this in your list of references.

If you find a source that is relevant to your research question by following the references and citations of the papers in your set of papers created after screening (a process known as snowballing or citation tracking, among other terms) then you should assess this according to your screening criteria.

If you discover relevant papers through citation tracking, or by chance, when you are scoping your search before doing the full literature search you should consider deep seed article analysis to expand your keywords. If the papers you've discovered do not appear in your literature search it is likely that other similar papers don't appear.  Using deep seed article analysis to ensure a thorough range of keywords is discussed at this point in my Systematic Literature Review training for social sciences researchers.

Contact your Academic Liaison Librarians for further advice on referencing or searching for a systematic review.