"The main reason why Poland is projected not to do too well in the future is the expected demographic decline. The model assumes that the fertility rate in Poland will remain low at 1.3 and that there will be no immigration. Both assumptions are incorrect.
First, the fertility rate in Poland is already increasing, exceeding 1.4 in 2009, up from 1.3 in 2003. What is more important, pressed by the society and rising future pension costs, the Polish government will have no choice, but to enhance its pro-family policy
Second, Poland is set to become a big recipient of immigrants, reversing the 300 year old trend. This is because with rising income Poland will become more and more attractive. When Poland's GDP per capita rises above 70% of the EU average, similarly to Spain in the mid-1990s and the Czech Republic recently . . ."
This would seem to be a general concern about these predictions - that population growth is actually hard to predict, and any forecasts done on the assumption that growth rates will remain stable or only change linearly are bound to be inaccurate. Something worth considering, for example, is that the UK's recent increases in birth rate have come at the expense of Eastern European states, where large numbers of young people emigrated to the UK after the accession of these states to the EU. Now that these states are becoming relatively richer, it seems unlikely that such migration patterns will continue.