Table 2. Multivariate negative binomial regression of the association between rate of self-reported respiratory infection and covariates, voluntary respiratory questionnaire data Jan 2005 to Jan 2006.

Covariate	IRR	(95% CI)	P-value
Branch
Army, Air Force, Marines	Reference
Navy	1.81	(1.36–2.40)	<0.001
Rank
E1–E4	Reference
E5–E6	1.18	(0.99–1.39)	0.06
E7–E9	1.47	(1.09–1.98)	0.01
Officer/CWO	1.75	(1.36–2.25)	<0.001
Sex
Male	Reference
Female	1.33	(1.10–1.61)	0.004
Operation
Enduring Freedom/Other	Reference
Iraqi Freedom	1.12	(0.96–1.30)	0.14
Latrine type
Flush	Reference
Chemical/burn	1.50	(1.30–1.73)	<0.001
Bag/trench/other	1.66	(0.89–3.10)	0.1
Per year of age increase	1.01	(0.99–1.02)	0.07
Tobacco Use (smoking)
None	Reference
1/2 pack per day (PPD)	1.10	(0.91–1.33)	0.3
1 PPD	1.19	(0.96–1.46)	0.1
More than 1 PPD	1.16	(0.80–1.68)	0.4