We investigate the group processes involved in effort estimation in the context of project management. The groups considered are formed by ‘‘experts’’ (people with specific technical competence) and ‘‘nonexperts’’ people with less specific technical competence, usually experts in related fields), because th  typically complementary bias of the two classes contribute to a more balanced estimate. In this paper we exploit further the synergies between experts and non-experts in an MCDM framework, aggregating the individual estimates by means of non-additive Choquet integration, and representing the complementary bias by the multiagent interaction structure underlying the capacity. We present some examples and computer simulations whose aggregation results outperform those of the classical weighted mean additive case), showing lower MMRE (mean magnitude of the relative error between the central estimate and the actual value) and higher HitRate (at which the interval estimate contains the actual value).