We provide results on the computational complexity of goodness of fit measures (i.e. Afriat's efficiency index, Varian's efficiency vector-index and the Houtman-Maks index) associated with several revealed preference axioms (i.e. WARP, SARP, GARP and HARP). These results explain the computational difficulties that have been observed in literature when computing these indices. Our NP-Hardness results are obtained by reductions from the independent set
problem. We also show that this reduction can be used to prove that no constant factor approximations algorithm exists for Varian's index, nor for Houtman-Maks' index (unless P = NP). Finally, we give an exact polynomial time algorithm for finding Afriat's efficiency index.