Could/should scholarly book chapters and published theses (dissertations) be included in the literature review as sources? In theory, those are scientific publications, right? However, those are also usually based on previously published work.
(Almost) everything is based on previously published work! But I think maybe you are referring to what we call the "secondary literature", which is review articles, books etc that don't present novel research (the "primary literature") but rather summarise or package up other research articles.
Yes, secondary literature can certainly be included in a literature review, especially if it gives ideas/opinions that have not been prominent elsewhere. However, if you refer to particular results then these should always refer back to the primary literature, even if you also give a mention to how those results have been described or discussed in the secondary literature.
(Note that dissertations/theses very often fall under the category of primary literature, in fact in some areas it is a requirement that they include novel research)
Yes, book chapters and theses are valid for a literature review.
You did not explain in your question why you questioned they might be; perhaps it is because they are included less frequently than journal articles and conference articles in literature reviews, so you might question their appropriateness. Here are a few practical reasons I can think of why they tend to be included less frequently:
- Journal articles and conference articles are much better indexed in scholarly databases, and so are easier to find. Book chapters are especially hard to find since they are rarely available online for free. (Theses, though, are relatively well-indexed these days, and they are usually freely available, unlike many journal articles.)
- The peer review standards for journal articles and conference articles are usually stricter, and so, in general, their quality tends to be higher on average than for book chapters and theses (of course, exceptions abound). In particular for theses, the better ones are often republished as journal articles after going through significant quality improvements in the peer review process. However, this is probably not the case most of the time--many theses are never republished as journal articles: some disciplines prefer publishing them as scholarly books, and some PhDs do not eventually republish their thesis in journals for various reasons.
- Theses are much longer and thus harder to read; so, expecially considering the fact two prior points, they are not worth the extra effort looking for (except if you know somehow in advance that the relevant thesis you seek actually exists somewhere).
However, despite these points, if you find book chapters or theses that are relevant to your literature review topic, do not hesitate to include them in your literature review.