RT Article T1 On the treatment of non-original sample members in the German household panel study (SOEP) JF Methoden, Daten, Analysen VO 2 IS 2 SP 179 OP 198 A2 Kroh, Martin LA English YR 2008 UL https://krimdok.uni-tuebingen.de/Record/1624954847 K1 Panelstudie K1 Stichprobe