Systematic methods for data reduction have been developed for the dual rotating-compensator ellipsometer in the PC(1r)(omega(1))SC(2r)(omega(2))A configuration, where P, C(1r)(omega(1)), S, C(2r)(omega(2)), and A represent the polarizer, first rotating compensator, reflecting sample, second rotating compensator, and analyzer, respectively. The approach used here is more general than previous treatments in that it incorporates dichroic compensators that rotate synchronously at a frequency ratio omega(1):omega(2) of p:q, where p and q are integers. For specific frequency ratios, the 24 ac Fourier coefficients of the irradiance waveform at the detector over-determine the 15 real elements of the (1,1)-normalized Mueller matrix and the 3 complex elements of the (2,2)-normalized Jones matrix. Alternative data reduction approaches resulting from this capability of over-determination are shown through numerical simulations to have different performance characteristics under non-ideal experimental conditions. Finally, the importance of using an achromatic retarder design in the dual rotating-compensator ellipsometer is emphasized through these simulations. (C) 2010 Elsevier B.V. All rights reserved.