A lithographic process is one that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. During the lithographic process, the focus should be controlled. There is disclosed a method for determining a fingerprint of a performance parameter associated with a substrate, such as a focus value to be used during the lithographic process. A reference fingerprint of the performance parameter is determined for a reference substrate. A reference substrate parameter of the reference substrate is determined. A substrate parameter for a substrate, such as a substrate with product structures, is determined. Subsequently, the fingerprint of the performance parameter is determined based on the reference fingerprint, the reference substrate parameter and the substrate parameter. The fingerprint may then be used to control the lithographic process.