In this fourth edition of the book, new features have been added in response to developments in research and reader feedback: • Throughout the book, I have cited updated editions of research methods books to emerge since the last edition. • To reflect current thinking about worldviews, I have expanded the participatory worldview, discussed in the last edition, to include a much broader worldview perspective—the transformative worldview—based on recent scholarship (Mertens, 2009, 2010). • There is updated information included in this edition on the Publication Manual of the American Psychological Association (American Psychology Association [APA], 2010).