Q: what are the types of background research in a thesis?

This question focuses on how to present data from prior, similar investigations. 

The foundation of an article’s results derives entirely from the focus of prior research. Please allow me here emphatically to urge you to act always to ensure that you build your research investigation on the strongest of foundations … that is, present a systematic and transparent review of previous, similar studies before you embark on any new investigations. Doing so is the initial step in reflecting ‘evidence-based research.’  

Editors and thesis advisors want to be sure that the literature cited is compelling, novel, timely, and accurate. If any of these standards are not met, then the structure might be viewed as inadequate. Your literature review should be highly selective and specific, referring only to work that is directly relevant to the argument you choose to make. A good literature review:

• Defines and clarifies a problem.
• Summarizes previous research to inform readers of research that is the extant.
• Identifies relationships, contradictions, gaps and inconsistencies and
• Suggests next steps.

Now, to specifically answer your question, it is up to you to choose the ‘quality’ (or ‘type’ as you have mentioned in your question) of the research that you will include in your review. For example, it is entirely appropriate to consider within the body of relevant literature that search engines pull up using keywords of your choice, only those articles which describe empirical data (rather than opinion descriptions), articles which include an indication of effect-size, research in a language that you can understand, manuscripts which describe data consistent with your sample, etc.

Note that at every step it is important to document for yourself the criteria that you are using to qualify/disqualify sets of identified literature from the past so that later you can transparently describe the nature of the literature for which you are providing a digest. It is of utmost importance to provide in your review a description of the research-selection process that you followed. Here, you need to describe the criteria you used to select the articles which you are reviewing. This requires you to disclose your keywords, the exclusionary criteria, and all the filters that you used to refine the set to the manageable number that you describe in your literature review.

Caven S. Mcloughlin, Ph.D., Editor-in-Chief Emeritus for a major commercial academic publisher.