Table 2.
Odds ratios and 95% confidence intervals for three logistic regression analyses to identify characteristics of farms with very large contact chains. The response variable is whether or not farms have (a) ICCs, (b) OCCs, and (c) ICCs and OCCs containing over 10 000 farms (values from combined 24 monthly-spaced chains). Herd size has been mean centred and is displayed for increments of 10 cattle (see electronic supplementary material, figure S7 for further herd size analysis).
| response variable | explanatory variable | levels | odds ratio | 2.50% | 97.50% |
|---|---|---|---|---|---|
| (a) ingoing contact chain greater than 10 000 | (intercept) | 0.151 | 0.131 | 0.172 | |
| herd size (per 10 cattle) | 1.004 | 1.002 | 1.006 | ||
| herd type | dairy | Ref | |||
| fat | 9.509 | 8.659 | 10.454 | ||
| mixed | 1.280 | 1.162 | 1.411 | ||
| suckler | 1.281 | 1.189 | 1.381 | ||
| region | east of England | Ref | |||
| east Midlands | 1.187 | 1.036 | 1.362 | ||
| northeast | 1.517 | 1.302 | 1.769 | ||
| northwest | 1.463 | 1.288 | 1.665 | ||
| Scotland | 0.767 | 0.677 | 0.872 | ||
| southeast | 0.297 | 0.251 | 0.350 | ||
| southwest | 0.577 | 0.509 | 0.656 | ||
| Wales | 0.484 | 0.425 | 0.553 | ||
| West Midlands | 1.073 | 0.942 | 1.225 | ||
| Yorkshire | 1.532 | 1.344 | 1.748 | ||
| herd type: fat | herd size (per 10 cattle) | 1.186 | 1.176 | 1.196 | |
| herd type: mixed | herd size (per 10 cattle) | 1.052 | 1.047 | 1.057 | |
| herd type: suckler | herd size (per 10 cattle) | 1.046 | 1.043 | 1.049 | |
| (b) outgoing contact chain greater than 10 000 | (Intercept) | 0.211 | 0.161 | 0.272 | |
| herd size (per 10 cattle) | 1.010 | 1.008 | 1.012 | ||
| herd type | dairy | Ref | |||
| suckler | 0.093 | 0.087 | 0.100 | ||
| mixed | 0.112 | 0.101 | 0.123 | ||
| fat | 0.051 | 0.046 | 0.057 | ||
| region | east of England | Ref | |||
| east Midlands | 1.526 | 1.153 | 2.047 | ||
| northeast | 11.584 | 8.817 | 15.442 | ||
| northwest | 18.075 | 14.009 | 23.716 | ||
| Scotland | 15.212 | 11.815 | 19.923 | ||
| southeast | 0.961 | 0.713 | 1.308 | ||
| southwest | 2.534 | 1.963 | 3.326 | ||
| Wales | 2.305 | 1.780 | 3.034 | ||
| West Midlands | 1.878 | 1.439 | 2.489 | ||
| Yorkshire | 3.646 | 2.796 | 4.828 | ||
| herd type: fat | herd size (per 10 cattle) | 1.011 | 1.006 | 1.016 | |
| herd type: mixed | herd size (per 10 cattle) | 1.040 | 1.035 | 1.045 | |
| herd type: suckler | herd size (per 10 cattle) | 1.041 | 1.038 | 1.044 | |
| (c) ingoing and outgoing contact chains greater than 10 000 | (Intercept) | 0.025 | 0.016 | 0.036 | |
| herd size (per 10 cattle) | 1.003 | 1.001 | 1.006 | ||
| herd type | dairy | Ref | |||
| fat | 0.493 | 0.433 | 0.561 | ||
| mixed | 0.496 | 0.428 | 0.574 | ||
| suckler | 0.372 | 0.335 | 0.412 | ||
| region | east of England | Ref | |||
| east Midlands | 1.153 | 0.739 | 1.853 | ||
| northeast | 8.152 | 5.463 | 12.674 | ||
| northwest | 10.429 | 7.163 | 15.909 | ||
| Scotland | 6.360 | 4.371 | 9.696 | ||
| southeast | 0.383 | 0.215 | 0.678 | ||
| southwest | 2.263 | 1.545 | 3.468 | ||
| Wales | 1.197 | 0.801 | 1.863 | ||
| West Midlands | 2.156 | 1.447 | 3.347 | ||
| Yorkshire | 3.358 | 2.265 | 5.195 | ||
| herd type: fat | herd size (per 10 cattle) | 1.020 | 1.014 | 1.025 | |
| herd type: mixed | herd size (per 10 cattle) | 1.031 | 1.025 | 1.036 | |
| herd type: suckler | herd size (per 10 cattle) | 1.034 | 1.030 | 1.037 |