Table 1. Characteristics of study participants in each survey.

Characteristics		2004 (N=32,793)	2007 (N=47,839)	2010 (N=90,196)	2013 (N=156,927)	2015 (N=162,055)	2018 (N=155,413)	p for trend
Men, %		44.3	47.3	45.6	42.3	46.0	43.7	0.5249
Age group, %	18-29 years	11.9	13.1	16.1	8.9	9.8	6.2	0.1269
	30-39 years	26.3	24.1	19.7	14.4	13.4	11.6	0.0004
	40-49 years	27.4	25.4	27.3	27.5	24.7	20.9	0.1251
	50-59 years	21.6	23.2	22.9	27.9	27.3	30.2	0.0042
	60-69 years	12.7	14.1	14.0	21.2	24.8	31.2	0.0048
Mean age (SD), years		44.1 (12.2)	45.0 (12.7)	44.3 (13.1)	48.9 (12.2)	49.4 (12.6)	51.9 (12.0)	0.0070
Urban, %		37.5	38.9	39.2	41.5	42.7	45.5	0.0012
Region, %	Central	10.8	13.2	13.5	12.4	12.3	12.8	0.4669
	East	23.1	24.9	24.1	26.0	25.3	24.8	0.1694
	North	12.9	14.2	14.2	14.7	14.3	14.7	0.0477
	Northeast	12.6	10.7	11.2	9.7	9.6	9.5	0.0139
	Northwest	15.2	12.3	12.3	13.0	13.2	13.2	0.4855
	South	8.9	8.8	8.5	9.8	9.9	10.2	0.0372
	Southwest	16.5	15.9	16.3	14.4	15.3	14.8	0.0592
Education, %	No education	18.6	24.9	21.6	25.2	26.1	26.3	0.0539
	Primary	29.1	19.6	19.3	19.9	20.1	19.5	0.1549
	Secondary	32.6	32.4	33.4	33.3	32.5	32.5	0.9848
	Collge	19.6	23.1	25.7	21.6	21.3	21.7	0.9206
Occupation, %	Agriculture related	56.6	48.9	47.7	47.3	45.8	44.3	0.0161
	Other manual work	5.7	6.9	4.1	4.8	4.1	3.5	0.0580
	Non-manual work	19.8	27.0	38.0	38.2	38.4	38.0	0.0269
	Not working	10.8	9.4	3.5	2.9	4.2	4.9	0.0768
	Retired	7.1	7.8	6.7	6.8	7.4	9.4	0.2747