  The price of anarchy, originally introduced to quantify the inefficiency of
selfish behavior in routing games, is extended to mean field games. The price
of anarchy is defined as the ratio of a worst case social cost computed for a
mean field game equilibrium to the optimal social cost as computed by a central
planner. We illustrate properties of such a price of anarchy on linear
quadratic extended mean field games, for which explicit computations are
possible. Various asymptotic behaviors of the price of anarchy are proved for
limiting behaviors of the coefficients in the model and numerics are presented.
