Appendice metodologica. Finalità e costruzione di un campionamento nel tempo: l’indagine panel

The paper reports the description of first wave of a longitudinal survey of textile and clothing firms in Emilia-Romagna (Italy), which was projected to be conducted using a “replenished” panel survey to produce reliable cross-sectional estimates. The firms (sampling units) were stratified according to size and age, and in all phases, dead and/or emigrated firms were considered as having already left the sample, while new units selected from newborn and immigrant firms, were considered as having already entered the sample. Population dynamics change firm composition over time and the methods of cross-sectional estimation must be adapted to the longitudinal features of the samples.