1-"A Quantitative Model-Independent Method for Global Sensitivity Analysis of
Model Output", A. SALTELLI, S. TARANTOLA, and K. P.-S. CHAN
2- "Importance measures in global sensitivity analysis of nonlinear models"
Toshimitsu Homma  & Andrea Saitelip
3- Metamodel-Based Sensitivity Analysis: Polynomial Chaos Expansions and
 Gaussian Processes" Loïc Le Gratiet, Stefano Marelli, and Bruno Sudret