On 2017 Dec 16, Wichor Bramer commented:

Dear Helge,

Thanks for your comment. Good to hear our research is helpful.

In our analysis we did not really differentiate between which specific database delivered the unique references that were coming from Web of Science. All I can see is the databases we subscribe to are these:

Science Citation Index Expanded (1975-present) Social Sciences Citation Index (1975-present) Arts & Humanities Citation Index (1975-present) Conference Proceedings Citation Index- Science (1990-present) Conference Proceedings Citation Index- Social Science & Humanities (1990-present) Emerging Sources Citation Index (2015-present)

I have the idea it is mostly the first two databases that contributed the most to the references, but that is only a wild guess and not at all based on objective research.

On 2017 Dec 15, Helge Knüttel commented:

This is a very nice and helpful work based on a broad empirical basis. It will have an impact on my future searching for systematic reviews.

The autors' main conclusion is that at least the databases/search engines Embase, MEDLINE (incl. ahead-of-print publications), Web of Science Core Collection and Google Scholar should be used for searching in a systematic review (plus some more depending on the topic). However, there is no data in the article what content contained in Web of Science (WoS) Core Collection contributed to the search results analyzed in the article. Therefore, it is not clear what content of Wos Core Collection the authors' recommendation relates to.

Web of Science Core Collection is a brand name for, well, a collection of databases. Currently, there are at least six citation indexes (Science Citation Index Expanded, Social Sciences Citation Index, Arts & Humanities Citation Index, Emerging Sources Citation Index, Book Citation Index, Conference Proceedings Citation Index) and two chemical indexes (Current Chemical Reactions, Index Chemicus) sold under the general term Web of Science Core Collection. These may contribute to relevant search results in highly varying degrees depending on the research question. This is of relevance as the set of databases accessible to a subscribing institution is not fixed. Rather, it is "You get what you pay for." In addition and unlike other databases a running subscription to one of the citation indexes will not give access to content from all previous years. "Archive" content will need to be purchased separately. As a result, the term "Web of Science Core Collection" may stand for a very broad range of database content.

It would be helpful if the authors could specify what WoS content their analysis and recommendation relates to.

On 2017 Dec 15, Helge Knüttel commented:

This is a very nice and helpful work based on a broad empirical basis. It will have an impact on my future searching for systematic reviews.

The autors' main conclusion is that at least the databases/search engines Embase, MEDLINE (incl. ahead-of-print publications), Web of Science Core Collection and Google Scholar should be used for searching in a systematic review (plus some more depending on the topic). However, there is no data in the article what content contained in Web of Science (WoS) Core Collection contributed to the search results analyzed in the article. Therefore, it is not clear what content of Wos Core Collection the authors' recommendation relates to.

Web of Science Core Collection is a brand name for, well, a collection of databases. Currently, there are at least six citation indexes (Science Citation Index Expanded, Social Sciences Citation Index, Arts & Humanities Citation Index, Emerging Sources Citation Index, Book Citation Index, Conference Proceedings Citation Index) and two chemical indexes (Current Chemical Reactions, Index Chemicus) sold under the general term Web of Science Core Collection. These may contribute to relevant search results in highly varying degrees depending on the research question. This is of relevance as the set of databases accessible to a subscribing institution is not fixed. Rather, it is "You get what you pay for." In addition and unlike other databases a running subscription to one of the citation indexes will not give access to content from all previous years. "Archive" content will need to be purchased separately. As a result, the term "Web of Science Core Collection" may stand for a very broad range of database content.

It would be helpful if the authors could specify what WoS content their analysis and recommendation relates to.