This paper analyses the reliability and accuracy of the relationships between migration and employment status when estimated using a linked data set. The analysis will be carried out using a new source, the "Labour and Geographical Mobility Statistics," which is provided by the Spanish Statistical Office. This statistic is constructed by an exact matching procedure, linking the "Labour Force Survey" with the Official "Population Register." The findings reveal that in order to accurately study geographic labour mobility, timing and geographical coherence between the two data sets must exist. If this is not the case, causality relations between the labour market and geographical mobility cannot be properly analysed. Although our analysis refers to the microdata quality and internal coherence of this new Spanish statistic, our conclusion can be extended to any linked data set for studying geographic labour mobility, including the population censuses mainly based on administrative data.