Kreyenfeld, Michaela, Kryštof Zeman, Marion Burkimsher, and Ina Jaschinski. “Fertility Data for German-Speaking Countries:What Is the Potential? Where Are the Pitfalls?”. Comparative Population Studies 36, no. 2-3 (January 18, 2012). Accessed September 29, 2020. https://www.comparativepopulationstudies.de/index.php/CPoS/article/view/62.