Galimberti, F., A. Fabiani and S. Sanvito (2003). Socio-spatial levels in linearity analysis of dominance hierarchies: a case study on elephant seals. Journal of Ethology 21: 131-136. The analysis of linearity is a key aspect of the study of dominance hierarchies. To study the effect of the choice of socio-spatial level of analysis, we calculated linearity in a large set of southern elephant seal (Mirounga leonina) hierarchies from two populations (Valdés Peninsula and Falkland Islands). The socio-spatial level of analysis affect the observational effort, the completeness of matrices, and the frequency of unknown relationships. These factors, in turn, have a notable effect on linearity. We conclude that dominance should be studied at local level, where the absence of structural zeros, and the low incidence of observational zeros, produce complete matrices, well rooted in the true spatial and social structure of the population. Depending on the specific social system, the extrapolation of dominance from the local level to higher levels may result in sparse matrices, and in biased estimates of linearity. The variation of the socio-spatial level of analysis may in part explain the contrasting results obtained in different studies of linearity of dominance hierarchies.