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Agreement (mean ± 95% CI) of OPA titers compared to the median OPA titers given in Table 1. The level of agreement to the median was determined in 2 by 2 tables with the formula a/(a + c), where a is the number of sera at or above the given titer by both the test laboratory and the median and c is the number of sera below the given titer by the test laboratory but at or above the given titer by the median.
