This book advances the methodology for measuring human capital attributes. Using Multidimensional Item Response Theory as a methodological paradigm, contemporary approaches to validity in educational research as a theoretical framework, various datasets from national and international educational assessments, and statistical simulations, the author provides an original solution to a nearly century-old problem in the psychometric modeling of composite competences, enabling an in-depth analysis of their structure. The comprehensive analyses presented in this book make a promising contribution to all research fields related to human capital by enabling advanced investigation of composite constructs. The book also offers recommendations for investigating complex generic and domain-specific competences, thus enhancing evidence-based practice and policy in education.