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Data and
Statistics > Immunization Coverage in the U.S.
How to use the NIS data
The National Immunization Survey (NIS) has a sample size of about 30,000
children. However, the sample is not the entire population, and thus sample
estimates and population values are likely to be different. The magnitude of
the likely difference is quantified through the 95% confidence interval. For
example, in 1998, the vaccination coverage estimate for 3 doses of
poliovirus vaccine in Alabama was 91.4% +- 3.2%. This means that the true
coverage was probably between 88.2% and 94.6%. When comparing two estimates
(e.g., between states or between years), an overlap in the confidence
intervals indicates that the observed difference might be due to chance.
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