3.2. Model-Dependent Determinations
The following derivations of the mass density parameter are based on
the hierarchical clustering model
of cosmic structure formation assuming the cold dark matter dominance.
The extraction of 
is,
therefore, indirect, but on the
other hand, it is reasonable to appeal to such models since
is
the parameter that predominantly controls structure formation.
Note that CDM model is the only model known today that successfully predicts
widely different observations, yet there are no observations strong
enough to refute its validity. We do not discuss
results from cosmological models where physical processes
other than gravity play a major role.