Data fusion enables the integration of multiple sensing data associated with the same physical process for more comprehensive process representation, thereby improving quality control in manufacturing. Based on a correlation analysis of measurement data, the effectiveness of data fusion has been investigated, using precision injection moulding as an application context and the predicted weight of moulded parts as a criterion. The study systematically explains why a multivariate sensor that quantifies four parameters at the same sensor location has consistently outperformed multiple single-parameter commercial sensors under various operation conditions, thereby contributing to the theory of data fusion for measurement enhancement.