What sources does the author use?
Check the foot- or endnotes or look at the reference list. Knowing where the author got the information and what sources were used will tell you whether the author is looking at something new (interviews, letters, archival or government documents, etc.), taking a new look at something old (books and articles), or combining new and old and thus adding to the discussion of the subject. Looking at the sources can show if the author has concentrated on a particular kind of information or point of view.