Hi,

BAMF (Bundesamt für Migration und Flüchtlinge - Federal Agency of Migration and Refugees) in Germany gives most accurate, official and actual statistical/academic/demographics analyses on foreigners in Germany. It belongs to BMI (Bundesministerium des Inneren - Federal Ministry of the Interior).

They have very interesting research documents that are available to public:
http://www.bamf.de/cln_101/nn_441764/DE/Service/Publikationen/publikationen-node.html?__nnn=true

Some examples for you:
Migrationsbericht 2005
http://www.bamf.de/cln_101/SharedDocs/Anlagen/DE/Migration/Publikationen/Forschung/Migrationsberichte/migrationsbericht-2005,templateId=raw,property=publicationFile.pdf/migrationsbericht-2005.pdf

The page 77 in the document above includes last statistics about Greencard people. The forum member "-" had asked for such a document before, for juristic reasons: http://trust7.com/en/foren/integration/90_of_gcs_have_left_the_country_is_that_true

Migrationsbericht 2007
http://www.bamf.de/cln_101/nn_442016/SharedDocs/Anlagen/DE/Migration/Publikationen/Forschung/Migrationsberichte/migrationsbericht-2007,templateId=raw,property=publicationFile.pdf/migrationsbericht-2007.pdf

In this report it was mentioned in Page 90 that a research for Niederlassungserlaubnis für Hochqualifizierte was done (AufenthG §19 Abs. 2 Nr 3).
I have mentioned that in the following post:
http://trust7.com/en/foren/integration/ne_for_highly_skilled_anual_salary_63000_euro/re_ne_for_highly_skilled_anual_salary_63000_euro__133

Our forum member rajeshspg participated that research:
http://trust7.com/en/foren/integration/ne_for_highly_skilled_anual_salary_63000_euro/re_ne_for_highly_skilled_anual_salary_63000_euro__146

Klenze17.