Known for its coherent overview of research methodology, Leary uses variability as an integrative theme, covering both experimental and non-experimental methods, including advanced topics.

Starting from the proposition that psychology is the study of behavioral variability, Leary uses the integrative theme of variability to demonstrate that all aspects of the research process attempt to answer questions about variability. This approach provides greater coherence and gives students a heuristic for thinking about problems they encounter in research. All major methods and designs are covered, including descriptive, correlational, experimental, and quasi-experimental approaches. While basic methods receive considerable coverage, the inclusion of more advanced topics, such as cross-lagged panel designs, factor analysis, meta-analysis, and structural equations modeling, allows for different levels of teaching and learning.