1. A computer implemented method of allocating human resources to a client at a plurality of levels, across sites, tiers and time periods, on business transformation outsourcing projects, the method comprising the steps of: modeling a human resources delivery services from a services provider to a client company to determine outputs from inputs and constraints; constructing an objective function representative of services resources at said services provider, including the step of constructing an optimization model for optimizing one or more defined objectives, said optimization model having parameters and constraints, and being nonlinear, noninteger and smooth, said optimization model comprising a set of formulas including a number of variables, wherein said number of variables include a plurality of levels of human resources across sites, tiers, and time periods for the client; determining optimum levels of human resources for the client based on said modeling, said constraints, and said objective function, including the steps of: solving, using a computer system, the optimization model using determined values for the parameters and constraints of the optimization model, including adjusting some of the parameters and constraints of the optimization model, and estimating a valid range for each of the parameters and constraints of the optimization model, solving the optimization model at various points across the ranges of the constraints of the optimization model to produce a solution to the optimization model, including identifying a set of values for said plurality of levels of human resources wherein, when said set of values are used in the optimization model, the optimization model maximizes or minimizes a specified one of the defined objectives, identifying leverage points in said solution, said leverage points being small changes in parameters and constraints that produce large changes in said one or more defined objectives, and determining whether selected changes in the leverage points are acceptable to the client company and to the service provider according to defined criteria; and allocating said human resources based upon said optimum levels; and wherein: said sites include both the client's and the services provider's locations; the service tiers include experts, specialists, generalists, and self-service; the constraints of the optimization model include: a lower bound on full time equivalent resources (FTEs) by site and tier that the client selects to retain as employees; and upper and lower bounds on FTEs by site and tier determined by the services provider; and the parameters of the optimization model include: the clients original FTEs by site and tier; labor cost per FTE by site and tier; and work migration costs by site and tier.