An Attempt to Measure the Trends in Shadow Employment in Poland: The Transition Probabilities Out and into Shadow Employment Using the LFS Data Augmented by the Results of a Dedicated Survey Performed by CASE in 2007 - An Attempt to Measure the Trends in Shadow Employment in Poland : The Transition Probabilities out and into Shadow Employment Using the LFS Data Augmented by the Results of a Dedicated Survey Performed by CASE in 2007