Table 1.
Derivation of variables used in analyses (bolded) to investigate serological associations with BRD.
| Data/variable | Distribution/categories | Notes/usage in analyses |
|---|---|---|
| Virus-specific induction serology categorya (e.g. BoHV-1 induction) | 0 1 2 or 3 4 or 5 |
Variables included in analyses to measure associations between serostatus at induction and becoming a case |
| Virus-specific composite variablea (e.g. BoHV-1 composite) | No change Seroincrease Initially high Missing |
Derived from serology categories at induction and follow-up; used to describe and analyse change in serostatus between induction and follow-up See Table 2 for classification |
| Virus-specific collapsed compositea (e.g. BoHV-1 composite (collapsed)) | Collapsed version of composite variable | |
| No seroincrease | No change or initially high | |
| Seroincrease | Seroincrease | |
| Virus-specific seroconversiona (e.g. BoHV-1 seroconversion) | No Yes |
Derived from serology categories at induction and follow-up; used to describe and analyse change in serostatus between induction and follow-up but restricted to animals seronegative at induction |
| Number of viruses animal was seropositive to at induction | 0–4 | Derived from induction serology for all viruses: (BoHV-1, BVDV-1, BRSV & BPIV-3) |
| Number of viruses animal seroincreased for between induction and follow-up | 0–4 | Derived from virus-specific collapsed composite variable for all viruses: (BoHV-1, BVDV-1, BRSV & BPI-3) |
a
Separate variables for each of the four viruses investigated: bovine herpesvirus 1 (BoHV-1), bovine viral diarrhoea virus 1 (BVDV-1), bovine respiratory syncytial virus (BRSV) and bovine parainfluenza virus 3 (BPIV-3).