Table 4. Multivariate negative binomial regression of the association between rate of self-reported respiratory infection and covariates, Qatar Clinic health screening questionnaire Feb 2005 to Feb 2006. (n = 14,361).

Covariate	IRR	(95% CI)	P-value
Age (per year increase)	1.02	(1.0–1.03)	<0.001
Sex
Male	Reference
Female	1.44	(1.21–1.73)	<0.001
Rank
E1–E3	Reference
E4–E6	1.29	(1.02–1.62)	0.04
E7–E9	1.11	(0.76–1.63)	0.6
O1–O3	1.16	(0.78–1.73)	0.5
O4–O6	1.52	(1.00–2.32)	0.048
Chief Warrant Officer	1.50	(0.76–2.95)	0.2