Table 3

Characteristics of farms excluded from the farm-level analyses due to missing data

Variable

Farm A

Farm B

Farm C

Farm D

Farm E

Manure spread on fields in summer season

No

---^a

---

---

---

Manure spread on fields in winter season

No

---

---

---

---

Manure stored on farm at any time of year

No

---

---

---

---

Other domestic livestock on farm

No

No

No

No

No

Other commercial poultry on farm

Yes

No

Yes

No

No

Farm has all-in-all-out policy

---

Yes

No

Yes

Yes

Farm water source

Official

Official

Official treated

Non-official

treated

Non-official

Number of houses on farm

1

1

2

2

1

Median flock size on farm

4019

1323

7971

4190

6728

Number of flocks raised

4

4

8

14

4

Number of positive flocks

3

1

2

5

1

^aData not available

Guerin et al. Acta Veterinaria Scandinavica 2007 49:18   doi:10.1186/1751-0147-49-18