We use linear and quasi-linear perturbation theory to analyse cold dark matter models of structure formation in spatially flat models with a cosmological constant .
Both a tilted spectrum of density perturbations and a significant gravitational wave contribution to the microwave anisotropy are allowed as possibilities .
We provide normalizations of the models to microwave anisotropies , as given by the four-year COBE observations , and show how all the normalization information for such models , including tilt , can be condensed into a single fitting function which is independent of the value of the Hubble parameter .
We then discuss a wide variety of other types of observations .
We find that a very wide parameter space is available for these models , provided \Omega _ { 0 } is greater than about 0.3 , and that large-scale structure observations show no preference for any particular value of \Omega _ { 0 } in the range 0.3 to 1 .