Table 1.
Model parameter estimates from multivariate Cox regression models using latitude or environmental parameters selected by the stepwise procedure as covariates for young oysters. The average of each environmental variable was calculated over the longest period preceding the mortalities (15 d for wild and 50 d for hatchery oysters).
| Parameter | Level | Df | Estimate | SE | χ2 | p | Odds ratio | 95% CI | |
|---|---|---|---|---|---|---|---|---|---|
| Model 1: Latitude and origin | |||||||||
| Latitude | 1 | −0.040 | 0.051 | 0.6 | 0.439 | ||||
| Origin | Hatchery | 1 | 6.823 | 2.971 | 5.3 | 0.022 | |||
| Wild | 0 | 0.000 | . | . | . | ||||
| Latitude × origin | Hatchery | 1 | −0.143 | 0.063 | 5.2 | 0.022 | 0.83 | 0.78 | 0.89 |
| Wild | 0 | 0.000 | . | . | . | 0.96 | 0.87 | 1.06 | |
| Model 2: Environment over the period preceding the mortalities and origin | |||||||||
| Origin | Hatchery | 1 | 0.059 | 0.029 | 4.2 | 0.040 | |||
| Wild | 0 | 0.000 | . | . | . | ||||
| Temperature (T) | 1 | −0.035 | 0.034 | 1.1 | 0.305 | ||||
| Food level (F) | 1 | 0.074 | 0.156 | 0.2 | 0.637 | ||||
| Rainfall (R) | 1 | 0.350 | 0.051 | 46.3 | <0.001 | 1.42 | 1.28 | 1.57 | |
| Sea level pressure (SLP) | 1 | 0.795 | 0.290 | 7.5 | 0.006 | ||||
| Wind speed (WNS) | 1 | 0.582 | 0.149 | 15.3 | <0.001 | ||||
| Origin × T | Hatchery | 1 | 0.357 | 0.045 | 63.2 | <0.001 | 1.38 | 1.30 | 1.46 |
| Wild | 0 | 0.000 | . | . | . | 0.97 | 0.90 | 1.03 | |
| Origin × F | Hatchery | 1 | 0.689 | 0.194 | 12.6 | <0.001 | 2.15 | 1.69 | 2.73 |
| Wild | 0 | 0.000 | . | . | . | 1.08 | 0.79 | 1.46 | |
| Origin × SLP | Hatchery | 1 | 1.649 | 0.293 | 31.7 | <0.001 | 11.52 | 6.80 | 19.52 |
| Wild | 0 | 0.000 | . | . | . | 2.22 | 1.26 | 3.91 | |
| Origin × WNS | Hatchery | 1 | 0.964 | 0.183 | 27.8 | <0.001 | 4.70 | 3.62 | 6.09 |
| Wild | 0 | 0.000 | . | . | . | 1.79 | 1.34 | 2.40 | |