A lithographic process is performed on a plurality of semiconductor substrates. The method includes selecting one or more of the substrates as one or more sample substrates. Metrology steps are performed only on the selected one or more sample substrates. Based on metrology results of the selected one or more sample substrates, corrections are defined for use in controlling processing of the substrates or of future substrates. The selection of the one or more sample substrates is based at least partly on statistical analysis of object data measured in relation to the substrates. The same object data or other data can be used for grouping substrates into groups. Selecting of one or more sample substrates can include selecting substrates that are identified by the statistical analysis as most representative of the substrates in their group and/or include elimination of one or more substrates that are identified as unrepresentative.