Abstract: In a manufacturing process using multivariate analysis for statistical process control, data representing a plurality of process and/or product variables is collected during operation of the process. A surrogate variable, representing the overall state of the process is evaluated. The surrogate variable is a function of a plurality of intermediate variables, which in turn are a function of the process and/or product variables. When the value of the surrogate variable is outside of a predetermined limit, the contributions to the surrogate variable by the intermediate variables are calculated. The intermediate variable with the largest contribution is identified and the contributions to the identified intermediate variable by the process variables is calculated., The process variables with the largest contribution to the identified intermediate variable are identified, and used to diagnose and correct the problem with the process.