Table 5.

Results of random-effects logistic regression (regression model 3 ‘thinning practice model’) investigating the effect of partial depopulation (thinning) on Campylobacter spp. colonization (defined as >123 000 c.f.u./g in pooled caecal samples) at depopulation. Results from a total of 888 batches sampled between 16 October 2011 and 31 August 2013 included in the UK poultry study on enhanced biosecurity and Campylobacter colonization; UK, 2011–2013

Factors	OR (95% CI)	P value
Practice of thinning
The flock had not been partially depopulated (78 batches)	1·00	0·004
The flock had been partially depopulated (thinned) (810 batches)	2·43 (1·34–4·42)
Sampling period
16 Oct.–30 Nov. 2011	0·63 (0·20–1·37)	0·245
1 Dec.–29 Feb. 2012	0·53 (0·30–0·93)	0·028
1 Mar.–31 May 2012	2·52 (1·40–4·43)	0·001
1 June–30 Aug. 2012	4·90 (2·60–9·21)	<0·001
1 Sept.–30 Nov. 2012	0·88 (0·50–1·49)	0·624
1 Dec.–28 Feb. 2013	1·00
1 Mar.–31 May 2013	1·69 (0·90–2·93)	0·064
1 June–30 Aug. 2013	1·57 (0·90–2·71)	0·101
Constant	0·66 (0·30–1·36)	0·263
Standard deviation of random effects	0·47 (0·26–0·85)
Interclass correlation coefficient (rho)	0·06 (0·02–0·18)

OR, Odds ratio; CI, confidence interval.