There are many challenges in evaluating the impact of books. Thus, the specific nature of books should be considered in the process of responsible evaluation.
The impact of scientific publications can often be measured by their citation impact. However, scientific books can often be very impactful, even outside of direct citations. Books are widely used in, for example, teaching and especially in theses. Books are also more widely read outside the academic world. Thus, books can have a significant impact long after they are no longer actively cited.
Evaluating the citation impact of books is a challenge. There is a limited number of scientific books in international databases. Where the coverage of databases is poor, individual citations can be very significant. Such variability can significantly distort the citation impact of books.
Google Scholar provides a more comprehensive coverage of books than the paid databases, but its indexing policy is not transparent. It is therefore not clear on what basis publications are indexed in Google Scholar. Google Scholar does not take the differences between fields of science and citation profiles into account, either. Google Scholar does provide a good overview of the citations received by books, but it is difficult to assess their significance.
Books often cover topics in a much broader way than individual articles. Books are also cited in a different way from articles, and citations to them often cover a complete subject area rather than individual observations. Although individual articles may cite a book in several parts of the article, these are counted as a single citation in the databases.
While articles usually have one clear final version (with the exception of articles in open access repositories such as arXiv, where there may be multiple and updating versions of articles), scientific books can have different editions and translations. Especially in the case of older books, scientific citations are usually to a more recent edition or translation. Evaluating the impact of these citations is not straightforward.