Disclosed herein is a quality control method for predicting premature degradation in mechanical properties of a series of moulded plastics components, the moulded plastics components being formed from a batch mixture comprising a cross-linkable polymer and a peroxide cross-linking agent. The method comprises selecting a subset of the series of moulded plastics components and obtaining a material specimen from the subset; and then extracting and measuring a residual peroxide content of the specimen. According to the invention,the measured residual peroxide content is representative of a probability of the premature age-related degradation in the entire series of moulded plastics components, and may therefore be compared against a threshold residual peroxide content to determine whether the entire series of components is of acceptable quality.