An apparatus and method for quantitatively ranking the performance of each attribute contributing to a manufacturing process. Various signals representing the measure (i.e., quality or yield) of a manufacturing run and representing the attributes that contributed to each manufacturing run are recorded. An iterative process is commenced whereby numeric weights are assigned to each attribute. In a first iterative step, the weight of each attribute is determined to be the weighted average of the measure of each manufacturing run to which that attribute contributed. In subsequent iteration steps, a refined weight for each attribute is determined by computing the ratio between the normalized measure and the product of all other weights associated with that manufacturing run. The iterations are continued until the weights determined for each attribute converge or become self consistent. In this manner, the performance of non-numeric or attribute parameters such as operators and tools can be measured and defined in terms of a numeric quantity.