||Potential non-response bias may increase as
there are expected increases in cell-phone only and broadband telephone
households. This may be particularly problematic if use of these types of
alternative phones is associated with race, education and poverty which are
also factors associated with immunization coverage. Another weakness of the
NIS is the inability of the NIS to measure coverage within IAP areas due to
the cost prohibitive nature of within state sampling. As discussed earlier,
measuring coverage on the local level is very important.