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The Plasmodium falciparum parasite rate (PfPR) is a commonly reported index of …

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- Standardizing estimates of the Plasmodium falciparum parasite rate


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Figure 1   The average distribution of sample sizes, S(A), from 21 studies that report PfPR by age, A. The lines show, by age, the mean (blue), the trimmed mean (red, with 10% of extreme values eliminated), the median (thick black), the interquartile range (thin black), and the 5th and 95th quantiles (dashed lines).

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Figure 2 The 21 training sets, ordered by peak PfPR. The PfPR data (black) have been plotted against the root of age in years, along with the confidence limits by the exact test for each proportion (grey). The maximum likelihood best-fit for the modified Pull & Grab model (orange) was also plotted; the plateau (horizontal dashed red line) and the age when PfPR begins to decline (vertical dashed red line) are indicated and the other fitted parameters are reported on each graph. The algorithm (blue) fitted to the data (i.e. four parameters were fixed at their trimmed mean values and the fifth parameter was fitted).  

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Figure 3   Theory predicts that the slope of PfPR in young children (i.e. b) and the PfPR in older children (i.e. the plateau, P') should be correlated. The best-fit parameters describing these two quantities are plotted here. Two extreme values were excluded from this plot. There was no correlation with (p = 0.23) or without (p = 0.56) the extreme values.

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Figure 4   Predicted PfPR plotted against observed PfPR for the four candidate algorithms for the testing set.

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Figure 5    The age-PR relationship as generated by the algorithm. Holoendemic areas are colored dark green, hyper-endemic areas green, meso-endemic areas light green, and hypoendemic olive.

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Figure 6   The graphs plot a subset of 87 PfPR estimates (i.e. PR1) in the testing set that were already standard (i.e. L1 ≥ 2 and U1 ≤ 10) and the predicted PfPR using either the PfPR pair (i.e. PR2, left) or the selected standardization algorithm (right). The dashed lines show the cutoffs for the classical categories [18]. The colors highlight properly classified hypoendemic (blue), mesoendemic (grey), and hyperendemic (orange) populations, as well as misclassified populations. Some mesoendemic populations were misclassified as hypoendemic (green) and some hyperendemic populations were misclassified as mesoendemic (orange). After standardizing, a few populations were mistakenly misclassified moved from hypoendemic to mesoendemic (cyan), or from mesoendemic to hyperendemic (tan). In sum, the PfPR would have been misclassified by the paired estimate (i.e. PR2) in 33/87 cases (38%). Using the selected Pull & Grab modified algorithm, the standardized values were misclassified in 16/87 cases (18%).


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