Table 2. Results from zero-inflated Poisson regression of number of IADL limitations on potential risk factors (n = 431).

I. Excess zeros: Prediction of having no IADL limitation	OR (95% CI)	SE	z	P
Age
< 50	1 (reference)
50–60	0.66 (0.24–1.78)	0.51	-0.82	0.410
> 60	0.04 (0.01–0.10)	0.54	-6.19	<0.001
Disease severity and age group
non-severe and < 50 years old	1 (reference)
severe and < 50 years old	0.06 (0.02–0.17)	0.51	-5.43	<0.001
non-severe and 50–60 years old	1 (reference)
severe and 50–60 years old	0.11 (0.04–0.32)	0.56	-4.02	<0.001
non-severe and > 60 years old	1 (reference)
severe and > 60 years old	0.34 (0.10–1.16)	0.62	-1.72	0.086
Province
Other provinces	1 (reference)
Hubei	0.09 (0.04–0.19)	0.37	-6.46	<0.001
Ethnicity
Han	1 (reference)
Tibetan	0.16 (0.06–0.41)	0.49	3.78	<0.001
Smoking history
no	1 (reference)
yes	1.78 (0.67–4.75)	0.50	1.15	0.251
Comorbid conditions
none	1 (reference)
one	0.65 (0.29–1.43)	0.41	-1.08	0.281
multi	0.33 (0.12–0.90)	0.51	-2.16	0.031
II. Count: Number of IADL limitations	IRR (95% CI)	SE	z
Disease severity (reference: non-severe)
non severe	1 (reference)
severe	1.64 (0.97–2.80)	0.45	1.84	0.066
Disease severity and age group
non-severe and < 50 years old	1 (reference)
non-severe and 50–60 years old	1.76 (0.99–3.15)	0.52	1.92	0.055
non-severe and > 60 years old	2.91 (1.78–4.77)	0.73	4.24	<0.001
severe and < 50 years old	1 (reference)
severe and 50–60 years old	1.34 (1.03–1.74)	0.18	2.21	0.027
severe and > 60 years old	1.65 (1.33–2.05)	0.18	4.52	<0.001
Symptoms, number
< = 1	1 (reference)
>1	1.34 (1.10–1.62)	0.13	2.98	0.003
Infection scope
Unilateral	1 (reference)
Bilateral	1.19 (0.89–1.61)	0.18	1.16	0.246

OR = odds ratio, CI = confidence interval, SE = standard error of coefficient, z = standardized coefficient, IRR = incidence rate ratio, IADL = instrumental activities of daily living.