We hypothesized that, within a primate group, socialization processes are influenced by each group member behaving according to his own social network. Therefore socialization processes would differ in various social environments. In this study, we considered two main socialization processes, the acquisition of a social behavioral repertoire and the development of a network of social relationships, and consequently defined six comprehensive developmental parameters. We analyzed the variability of these parameters using a new multifactorial method, the Principal Components Analysis with Instrumental Variable, PCAIV, derived from the Principal Components Analysis and Multivariate Analyses of Variance. This technique allowed us to jointly represent the influence of the independent variables and the complex relationships between the six dependent variables. The study of the social ontogeny of eight infant mangabeys (Cercocebus albigena), reared in three different social environments, served as an illustration of the use of the new multivariate analysis. A 3-variable-model (age, social environment and sex) significantly explained the variability of the developmental parameters. The results confirmed the importance of social interactions in non-human primate infants' development. The application of multivariate methods to the study of individual social development looks promising for future research.