In the Internet you can find several Open Access journals on leadership.

In these journals you can find book reviews of the books and articles by the topic you study. From journals' articles you can get an additional information of the topic, find new material about studies and works of researchers and practitioners.

Scientific information in the peer-reviewed journals has gone through a peer review process and is therefore highly recommended. 

You have read the book review of Peter G. Northouses (2009) Leadership: theory and practice by Susan Gibbons in International Journal of Leadership Studies (IJLS) while examining the content of the book.

In this journal you can also find articles about the topic Leadership Styles.

Please read the article in Volume 5, Issue 1 2009 Aggression, Risk Taking, and Leadership Effectiveness: Leadership Lessons From the Explanatory Styles of Civil War Generals by Jeffery D. Houghton from West Virginia University, United States and Timothy D. Johnson from Lipscomb University, United States. http://www.regent.edu/acad/global/publications/ijls/new/vol5iss1/IJLS_Vol5Is1_HoughtonJohnson%20(2)R.pdf

To get more information about the journal, please browse the web page.