Using Analysis of Gini (Anogi) for Detecting Whether Two Sub-Samples Represent the Same Universe : The SOEP Experience

A particular shortcoming of panel surveys is potential bias arising from selective attrition. Based on data from the German Socio-Economic Panel Study (SOEP) we analyze potential artifacts (level, structure, inequality of income) by comparing results from two independently drawn panel sub-samples, started in 1984 and 2000, respectively. Both sub-samples carried on using the same set of follow-up rules. We apply ANOGI (ANalysis Of GIni) techniques, the equivalent of ANOVA (ANalysis Of VAriance) performed on the basis of the Gini coefficient. The decomposition followed is presented in Yitzhaki (1994). We rearrange, reinterpret and use the decomposition in the comparison of sub-populations from which the different subsamples were drawn. Taking into account indicators for income, and for control purposes those for education and satisfaction as well, significant differences between these two subsamples with respect to (income) inequality are found in the first year, which start to fade away in wave 2 and disappear in wave 3. We find credible indication for these differences to be driven by changes in response behavior of short term panel members rather than by attrition among members of the longer running sub-sample