When analyzing spectroscopic ellipsometry data it can be difficult to find unique solutions if, for instance, the dielectric function of a film must be found together with the film thickness. One method to find the solutions is 'multiple sample analysis'. The basic assumption for this method is that the optical properties of the unknown layers are identical in all samples. In the analysis procedure a set of samples with different film thicknesses are prepared and measured, preferably at multiple angles of incidence. Several (one for each sample) identical optical models are then defined with coupled optical properties of the unknown lavers and all data are fitted simultaneously. This ill give solutions for the dielectric function of the films and the film thicknesses due to parameter decoupling. The analysis can also be extended to more complex samples including more than one film thickness, surface and interface roughness, and porosity. In this study we have applied the multiple sample analysis method to find dielectric functions, film thicknesses and surface roughnesses of thin films of Ta2O5, ScN and CeO2.