Table 5.

Interpretation of interaction terms in the logistic regression model comparing poultry that sampled positive for Newcastle disease (ND) (titre ⩾2⁴) to those that sampled negative for ND (titre <2⁴) (n = 20 490 poultry sampled)

Variable	Comparison	Interaction group	Odds ratio
Species	Ducks vs. chickens (reference: chickens)	Control	0·15*
		AI vaccination	1·16
		AI and ND vaccination	0·35
Age	Adult vs. young (reference: young)	Control	1·50
		AI vaccination	2·62
		AI and ND vaccination	2·19
Treatment	AI vaccination vs. control (reference: control)	Chickens	0·57
		Ducks	4·54
		Young	0·57
		Adult	1·00
	AI and ND vaccination vs. control (reference: control)	Chickens	2·43
		Ducks	5·80
		Young	2·43
		Adult	3·55

AI, Avian influenza, ND, Newcastle disease.

^*Odds ratio indicates that in the control group, the odds of ducks being seropositive for ND were 0·15 times the odds of chickens being seropositive.