Table 1.
A proportional hazard model investigating the effect of P. laevis infection, water quality and wounding on the survival of G. pulex. Parameter estimates (±s.e.) and risk ratios (with 95% CI) are given. The risk ratio refers to the increase in hazard function compared with the control group. A risk ratio value greater than 1 indicates that the mortality of the experimental group is higher than that of the control group. As an example, a risk ratio of 1.93 for the infection factor suggests that the overall hazard function for infected gammarids is increased by a factor of approximately 2.
| factors | estimate (±s.e.) | LR χ2 | d.f. | p-value | risk ratio (95% CI) |
|---|---|---|---|---|---|
| in the best modela | |||||
| infection | 0.66 (±0.07) | 77.08 | 1 | <0.0001 | 1.93 (1.66–2.24) |
| water | 0.60 (±0.07) | 65.83 | 1 | <0.0001 | 1.82 (1.57–2.11) |
| wound | 0.36 (±0.07) | 28.48 | 1 | <0.0001 | 1.44 (1.26–1.64) |
| water × wound | 0.18 (±0.06) | 7.74 | 1 | 0.0054 | 1.20 (1.06–1.37) |
| infection × water | 0.14 (±0.06) | 4.03 | 1 | 0.0447 | 1.15 (1.00–1.32) |
| not in the best model | |||||
| infection × water × wound | 0.07 (±0.06) | 0.96 | 1 | 0.3272 | |
| infection × wound | 0.06 (±0.06) | 1.05 | 1 | 0.3050 | |
aBest global model LR χ2 = 129.04, d.f.N = 5, d.f.D = 234, p < 0.0001.