The kind of research in which the major base of references and knowledge is from secondary sources such as census data, newspaper clippings, birth certificates and past records in different sectors, such a research is called archival research. Another name for archival research is secondary research, which is the opposite of primary research, which is research that is done from scratch and no past material is sought help from. In lieu original material is collected and researched over in terms of primary research. As far archival or secondary research, it is a relatively inexpensive process as compared to primary research. Nevertheless primary research has a more authentic aura in comparison to secondary research. Even there is a trepidation of incomplete or haphazard information in the case of archival research. For the alternative case, a type of research called naturalistic observation was used, which bears a whole set of differences with the secondary research.
I think the above guy means to say "the kind of research in which the major base of references and knowledge is from PRIMARY sources such as..."