Table 2. Results of the Average Nearest Neighbor (ANN) statistic performed on geographic and phylogenetic groupings of S. Typhi acute infections.
| Groupa | No. of pointsa | Ō distance (meters) | Ē distance (meters) | Nearest Neighbor Ratio (RN) | ANN Z-scoreb |
ANN P-valuec |
Fig C in S1 Text. Panel |
|---|---|---|---|---|---|---|---|
| All cases | 260 | 676.07 | 2312.04 | 0.29 | -21.83 | p<0.005 | A |
| Cases AUA | 42 | 204.87 | 331.34 | 0.62 | -4.73 | p<0.005 | A |
| Cases NWU | 110 | 351.30 | 858.30 | 0.41 | -11.85 | p<0.005 | A |
| Cases ROU | 55 | 607.40 | 2406.22 | 0.25 | -10.61 | p<0.005 | A |
| Cases SAV | 53 | 1800.82 | 3007.99 | 0.60 | -5.59 | p<0.005 | A |
| Cases 3.5.4.1 | 46 | 1589.89 | 3230.86 | 0.49 | -6.59 | p<0.005 | B |
| Cases 3.5.4.2 | 46 | 1211.20 | 2990.57 | 0.41 | -7.64 | p<0.005 | C |
| Cases 3.5.4.3 | 74 | 1710.15 | 3304.99 | 0.52 | -7.94 | p<0.005 | D |
ANN is a statistical comparison of the observed mean (Ō) and expected mean (Ē) distances between points yields a nearest neighbor ratio (Rn) further described by a probability (p-value) that the observed spatial pattern was created by a random process and standard deviations (z-score). The Rn ranges from 0 (indicating discrete clustering of points) to ~2.15 (indicating uniform dispersion of points equidistant from one another). An Rn value of 1 indicates complete spatial randomness.
a Only household coordinates of acute cases were included to assess circulating S. Typhi detected through routine passive surveillance and to avoid biasing the point-pattern analyses to households where asymptomatic shedders were localized by active investigation.
b All z-scores are small (<-1.96) corresponding to a confidence level above 95%.
c All p-values are small (<0.005) which indicate statistical significance.