A method, computer program and associated apparatuses for metrology. The method includes determining whether a substrate or substrate portion is subject to a process effect. The method includes: obtaining inspection data including a plurality of sets of measurement data associated with a structure on the substrate or portion thereof (for example measurement pupils); and obtaining fingerprint data describing a spatial variation of a parameter of interest. An iterative mapping of the inspection data to the fingerprint data is performed. Whether the structure is subject to a process effect is based on a degree to which the iterative mapping converges on a solution.