A method of determining a parameter of a lithographic apparatus, wherein the method includes providing first height variation data of a first substrate, providing first performance data of a first substrate, and determining a model based on the first height variation data and the first performance data. The method further includes obtaining second height variation data of a second substrate, inputting the second height variation data to the model, and determining second performance data of the second substrate by running the model. Based on the second performance data, the method determines a parameter of the apparatus.