If there is any software effort estimation technique for general development. if we are going to estimate the efforts when the mode of development is global. to what extent there can be impacts over the accuracy of estimation.
I think you should have historical record of the goodness of estimation done by the individual entities/teams/developers who participated in the project. The mean relative error may be useful for that. The productivity and estimation capabilities are known to vary about ten folds from a team to another. Hope this helps.