Distributions of MAT scores from the 1995–2005 time series. Part (a) shows the histogram of all 248 positive titers among the 724 samples that were measured to a maximum dilution of 1:204800. Parts (b) and (c) show distributions of different subdivisions of these 248 scores, represented as cumulative distribution functions that show the proportion of samples with scores less than or equal to a given value. Titer scores are represented as log2(MAT/100), such that a score of 0 corresponds to a titer of 1:100, a score of 1 to a titer of 1:200, etc. The highest score of 11 corresponds to titers ≥ 1:204800. Sample sizes for (c) are Jan-Mar (N = 21), Apr-Jun (N = 21), Jul-Sep (N = 115) and Oct-Dec (N = 91).