This book is a practical and theoretical guide that demonstrates how to leverage investment data in numerical models despite uncertainty and ambiguity. The author presents innovative methods that incorporate fuzzy set theory to overcome the imprecision of expert opinions and appraisals. Through real industry case studies and comparative analyses, the book provides a comprehensive understanding of how these novel approaches can be implemented to measure robustness. This book is a must-read for managers involved in investment decision making, for economists, lecturers, as well as M.Sc. and Ph.D. students studying investment decision-making.