tjalling c koopmans research institute utrecht school of economics university vredenburg 138 3511 bg the netherlands telephone 0031 030 253 9800 fax 7373 website www koopmansinstitute nl is and it was founded in 2003 named after professor dutch born nobel prize laureate 1975 discussion papers series publishes results ongoing for early dissemination to enhance with colleagues please sent any remarks or questions on this p vandriel econ uu ontwerp voorblad wrik how reach authors wolter hj hassink department tel email w michiel van leuvensteijn cpb bureau economic policy analysis hague 070 338 3488 m maastricht po box 616 6200 md paper can be downloaded at
