Abstract It is not easy to compare one statistic with another, and it is even more difficult if the analysis is based on two surveys that do not share the same issue, have different survey methods, and especially if the sample size of the surveys differ greatly. This paper will use a comparison of official and unofficial statistics, the micro-census and the German Socio-Economic Panel Study (SOEP) to confirm this point. An auxiliary structure for study of fertility behavior of women in Germany is conducted first with the micro-census and then with SOEP data. By that the transferability of a study model of the micro-census to the SOEP is examined. The SOEP provides the possibility to check the validity of the auxiliary structure which gives just an estimation of the current situation regarding the childlessness in Germany. The study model will be run for a second time with the SOEP data, however, this time not with the estimated number of mothers, but with the number actually recorded by the SOEP. Thus the quality of the estimation results can be checked.