Methods of determining information about a patterning process. In a method, measurement data from a metrology process applied to each of a plurality of metrology targets on a substrate is obtained. The measurement data for each metrology target includes at least a first contribution and a second contribution. The first contribution is from a parameter of interest of a patterning process used to form the metrology target. The second contribution is from an error in the metrology process. The method further includes using the obtained measurement data from all of the plurality of metrology targets to obtain information about an error in the metrology process, and using the obtained information about the error in the metrology process to extract a value of the parameter of interest for each metrology target.