Table 4

Six logistic models for farm-level factors associated with Campylobacter in broilers in Iceland (n = 28a)

Variable

Automated forward selection

Automated forward stepwise

Automated backward selection

Automated backward stepwise

Manual backward selection using "manure spread in summer"

Manual backward selection using "manure spread in winter"


Median flock size on farm (divided by 1,000)

0.10 (0.000)b

0.10 (0.000)

0.11 (0.000)

0.09 (0.001)

0.13 (0.000)

0.12 (0.000)

Farm water source

Non-official

Ref.

Ref.

Ref.

Ref.

Non-official treated

-0.57 (0.066)

-0.03 (0.913)

-0.50 (0.169)

-0.33 (0.370)

Official

-0.60 (0.051)

-0.76 (0.009)

-1.04 (0.004)

-0.99 (0.005)

Official treated

-0.87 (0.032)

-1.06 (0.006)

-1.21 (0.006)

-1.17 (0.007)

Other domestic livestock on farm

-0.65 (0.026)

-0.60 (0.028)

-1.01 (0.004)

-0.90 (0.004)

Other commercial poultry on farm

0.59 (0.000)

0.59 (0.000)

-0.72 (0.063)

-0.59 (0.097)

Number of houses on farm

0.06 (0.038)

0.13 (0.008)

0.11 (0.008)

Manure spread on fields in winter seasonc

0.54 (0.035)

1.90 (0.014)

Not included in model

0.97 (0.004)

Manure spread on fields in summer seasonc

-1.71 (0.028)

0.92 (0.025)

Not included in model

Manure stored on farm at any time of year

-0.83 (0.029)

-0.76 (0.025)

Farm has all-in-all-out policy

AICd of model

5.09

5.09

4.86

4.78

4.94

4.79


a Only farms with complete data for all variables are included

b Regression coefficient (p-value).

c Variables are highly correlated (τb ≥ 0.8)

d Akaike's Information Criterion

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

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