TABLE 8.
Comparison of logarithmically transformed (base 10) and raw Simpson index diversity values for water samples in which specific pathogens were present or absent
| Pathogen (no. of samples examined) | Mean Simpson index value ± 95% confidence interval of meana (no. of samples) |
Effect size index (d)b |
Pc |
|||||
|---|---|---|---|---|---|---|---|---|
| Log transformed |
Raw |
Log transformed | Raw | Log transformed | Raw | |||
| Presence | Absence | Presence | Absence | |||||
| Salmonella spp. (186) | 0.920 ± 0.089 (21) | 0.847 ± 0.034 (165) | 0.140 ± 0.048 (21) | 0.164 ± 0.015 (165) | −0.33 | −0.24 | 0.144 | 0.359 |
| Campylobacter spp. (182) | −0.937 ± 0.053 (38) | 0.832 ± 0.038 (144) | 0.126 ± 0.019 (38) | 0.171 ± 0.017 (144) | −0.48 | −0.46 | 0.002 | 0.001 |
| Cryptosporidium oocysts (153) | 0.833 ± 0.055 (74) | 0.870 ± 0.050 (79) | 0.174 ± 0.027 (74) | 0.156 ± 0.021 (79) | 0.16 | 0.17 | 0.317 | 0.290 |
| Giardia cysts (153) | 0.890 ± 0.078 (34) | 0.841 ± 0.042 (119) | 0.149 ± 0.028 (34) | 0.169 ± 0.020 (119) | −0.21 | −0.19 | 0.293 | 0.247 |
a
Simpson index diversity values for samples in which pathogens were present (Presence) or absent (Absence) were obtained with ERIC-PCR data. The 95% confidence interval of the mean was calculated by multiplying the standard error of the mean by 1.96.
b
Calculated as (μ1 − μ2)/σpooled. An effect size of 0.20 is considered small; 0.50, medium; 0.80, large (12).
c
By Welch's t test (for samples of unequal size and unequal variance) utilizing Satterthwaite's approximation for degrees of freedom. P values are 2-sided.