2.1. Occam's Razor
The above working hypotheses, and the order by which more specific models should be considered against observations, are guided by the principle of Occam's Razor, i.e., by simplicity and robustness to initial conditions. The caveat is that different researchers might disagree on the evaluation of ``simplicity''.
It is commonly assumed that the simplest model is the Einstein-deSitter model, m = 1 and = 0. One property that makes it robust is the fact that m remains constant at all times with no need for fine tuning at the initial conditions (the ``coincidence'' argument ).
The most natural extension according to the generic model of inflation is a flat universe, tot = 1, where m can be smaller than unity but only at the expense of a nonzero cosmological constant.
These simple models could serve as useful references, and even guide the interpretation of the results, but they should not bias the measurements.