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Disease Prevention |
Vaccination |
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Notes : Spearman-Karber calculation of PD50 |
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The extreme dilutions of the dose titration series should show 0% and 100% protection for the best use of this method, although an assumption can be made, if necessary, that either of these values lies beyond the end of the series. The only important effect of making such an assumption is that it will not be possible to deduce the true PD50. Rather, it will be necessary to express the calculated PD50 as equal to or greater than the observed value. Specimen Table Where k is the number of steps in the dilution series, pi and pi+1 are the proportions protected in doses i and i+1, and xi and xi+1 are log10 of the dilution factors for doses i and i+1. The calculation of (pi+1 - pi)(xi + xi+1)/2 is made for each dilution in the data set given above and the products summed to give the log10 PD50. This data set gives an arithmetic PD50 value of 7.23. |
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