Supersymmetric Grand Unified Theories and Global Fits to Low Energy Data

We present a self-consistent $\chi^2$ analysis of several supersymmetric (SUSY) grand unified theories recently discussed in the literature. We obtain global fits to low energy data, including gauge couplings, fermion masses and mixing angles, gauge boson masses and $BR(b\rightarrow s\gamma)$. One of the models studied provides an excellent fit to the low energy data with $\chi^2\sim 1$ for 3 degrees of freedom, in a large region of the experimentally allowed SUSY parameter space. We also discuss the consequences of our work for a general MSSM analysis at the $Z$ scale.