Er, you did know that those studies were all done under the restrictions that were not lifted until 2011 didn`t you ?
Since Sunday 1st May 2011, nationals of Czech Republic, Poland, Hungary, Slovakia, Slovenia, Estonia, Latvia and Lithuania – the so-called A8 countries which joined the EU in 2004 – are no longer restricted in their access to labour markets and state support systems across the European Union. In the UK context, this means that restrictions on access to work, housing rights and social benefits for A8 nationals have ceased to operate. They effectively now enjoy the same rights as other European Union nationals living in the UK.
Under the 2004 Accession Agreement, the 15 pre-existing EU member states were permitted to introduce transitional restrictions on A8 nationals, relating to their right to work and access state support on their territories. The UK was one of just three states to open its labour markets to A8 nationals in 2004. Other states were more cautious, maintaining tight restrictions on A8 workers for fear of labour market disruption for the first few years at least. By April 2011, Germany and Austria were the only EU countries to remain closed to A8 migrant workers.