  We present an analysis of the four-year data from the COBE DMR experiment. We
use a Karhunen-Loeve expansion of the pixel data to calculate the normalization
and goodness-of-fit of a range of models of structure formation. This technique
produces unbiased normalization estimates and is capable of determining the
normalization of any particular model with a statistical uncertainty of 7%. We
present a parameterization of the normalization and likelihood function which
summarizes our results for a wide range of models. We use the COBE
normalization to compute small-scale fluctuation amplitudes for a variety of
models and discuss the implications of these results for theories of
large-scale structure.
