This bestseller discusses regression modeling of clustered or hierarchical data, such as data on students nested in schools, patients in hospitals, or employees in firms. Assuming some knowledge of linear regression, it explains models and their assumptions, applies methods to real data using Stata, and shows how to interpret the results. This extensively revised second edition includes 3 new chapters, comprehensive updates for Stata 10, 38 new exercises, and 27 new data sets. The applications and exercises span a wide range of disciplines, including the medical, social, and behavioral sciences.