Diverging trends of chronic bronchitis and smoking habits between 1998 and 2010

Respiratory Research

Table 1 Distribution of the design variables

	ISAYA (1998/2000) N = 25,969	GEIRD (2007/2010) N = 18,357	p-value*
N° of responders (response rate, %)	18,873 (72.7)	10,494 (57.2)	<0.001
Season at time of the interview, %			<0.001
spring	18.5	41.0
summer	16.4	22.1
autumn	40.4	25.7
winter	24.7	11.2
Phone contact, %	27.9	11.8	<0.001
Females, %	50.7	52.3	0.008
Age (years), mean (sd)	33.1 (6.9)	34.7 (7.1)	<0.001

* p-value obtained by Pearson’s chi-squared test and two-sample t test with unequal variances.

ISSN: 1465-993X