The parameters used in Eq. \[NMRspectra\] are the same as the ones used in Ref. .

Note that the quantity usually identified experimentally as the Knight shift, the location of the peak in the NMR spectrum in Fig. \[NMR2\], does not match the global polarization. This Knight shift measurement always overestimates the global polarization. In order to obtain the global polarization of the system from the measured spectrum one has to extract the first moment of a normalized spectrum.[@Jairo] One sees from the NMR spectrum at $\gamma=1.25$ that disorder induced spin density variation leads to a broadening of the maximum peak and can even lead to secondary peaks at lower Knight shift frequencies. Note, however, that features corresponding to negative Knight shifts, corresponding to regions of reversed electronic spins, are unlikely because the typical size of such regions is small and because they are also obscured by the finite width of the quantum wells which trap the 2DES. Our calculations demonstrate that care must be taken in interpreting low temperature NMR data in the quantum Hall regime.

The partially polarized regime can also be studied experimentally by measuring the transport activation gap. Provided that weak Zeeman coupling can be ignored, 