BMC Public Health 2009, 9:130 http://www.biomedcentral.com/1471-2458/9/130 7%), arthritis (21% vs. 10%) and prostatisim (19% vs. 8%) was observed among those that reported poor sleep quality compared to those with good sleep quality (Table 2). Sleep quality: associated factors Based on the results of the univariate analyses -and previ- ous publications-, gender, region, residential status, BMI, alcohol consumption and smoking, physical activity, edu- cational level, marital status, medical insurance coverage, social activity, SRH, diabetes, CVD, arthritis, prostatisim, depressive symptoms and sleep quantity were chosen to be analysed in the multivariate analysis (Table 3). The results of the multivariate analysis indicated that gen- der (Odds Ratio (OR) 0.51; 95% Confidence Interval (CI) 0.41 to 0.64), region (OR 0.61; 95% CI 0.51 to 0.73), medical insurance coverage (OR 0.73; 95% CI 0.59 to 0.90), social activity (OR 0.80; 95% CI 0.69 to 0.94), res- idential status (OR 1.27; 95% CI 1.01 to 1.60), SRH (OR 2.48; 95% CI 2.08 to 2.96), depressive symptoms (OR 4.05; 95% CI 3.12 to 5.26), CVD (OR 4.05; 95% CI 3.12 to 5.26) and sleep duration (<7 hours daily sleep (OR 0.10; 95% CI 0.07 to 0.14), 7–9 hours daily sleep (OR 0.58; 95% CI 0.42 to 0.78)) affected the quality of sleep independently from the effect of other variables in the model (Table 3). When we stratified the analyses by region (Beijing/Shang- hai) we found that gender, depressive symptoms, self- rated health and sleep duration still remained signifi- cantly associated with sleep quality in both north and south China. Residential status, marital status, social activity and present CVD only affected the sleep quality of participants living in Shanghai, while arthritis only affected those living in Beijing (Table 3). Table 3: Adjusted associated factors of sleep quality for the total population and stratified by regional area of living Association with sleep quality (OR with 95% CI) Variable Gender (female vs. male) Residential location (rural vs. urban) Geographic location (Beijing vs. Shanghai) Body Mass Index (BMI) normal vs. over weight under weight vs. over weight Smoking current vs. never smoker former vs. never smoker Alcohol drinking (No vs. yes) Physical activity high vs. low moderate vs. low Educational level, years in school group 1 vs. 3 group 2 vs. 3 Marital status (no spouse vs. spouse) Medical insurance (no vs. yes) Employment employed vs. retired unemployed vs. retired Social activity (no vs. yes) Self rated health status (good vs. not good) Diabetes (no vs. yes) Cardiovascular disease (no vs. yes) Arthritis (no vs. yes) Depressive Symptoms (no vs. yes) Total hours of sleep/day <7 vs. 9< hrs 7–9 vs. 9< hrs Abbreviations: CES-D, Center for Epidemiologic Studies Depression Scale; OR, Odds ratio; CI, Confidence interval. *P < 0.05. Group 1, 2 and 3 for educational level are 0–6, 7–9 and ≥10 years in school respectively. Total 0.51 (0.41–0.64)* 1.27 (1.01–1.60)* 0.61 (0.51–0.73)* 0.92 (0.79–1.07) 0.74 (0.49–1.12) 0.90 (0.71–1.14) 0.98 (0.72–1.32) 0.97 (0.80–1.18) 1.09 (0.81–1.46) 0.94 (0.70–1.28) 1.24 (0.97–1.59) 1.06 (0.86–1.30) 1.25 (1.00–1.56)* 0.73 (0.59–0.90)* 1.05 (0.86–1.28) 1.00 (0.81–1.25) 0.80 (0.69–0.94)* 2.48 (2.08–2.96)* 1.01 (0.82–1.26) 1.47 (1.15–1.88)* 1.23 (0.99–1.53) 4.05 (3.12–5.26)* * 0.10 (0.07–0.14)* 0.58 (0.42–0.78)* Beijing 0.55 (0.40–0.75)* 1.08 (0.77–1.52) 1.05 (0.84–1.30) 0.35 (0.17–0.72) 0.79 (0.58–1.08) 1.15 (0.78–1.70) 0.95 (0.74–1.23) 0.93 (0.62–1.39) 0.81 (0.53–1.23) 1.38 (0.98–1.94) 1.13 (0.84–1.53) 1.14 (0.84–1.55) 0.84 (0.60–1.16) 1.07 (0.80–1.43) 0.80 (0.59–1.08) 0.83 (0.66–1.03) 2.25 (1.76–2.88)* 1.10 (0.84–1.44) 1.25 (0.92–1.71) 1.40 (1.04–1.89)* 3.91 (2.88–5.29)* * 0.10 (0.07–0.15)* 0.64 (0.44–0.92)* Shanghai 0.50 (0.36–0.71)* 1.66 (1.13–2.43)* 0.81 (0.65–1.01) 1.03 (0.60–1.76) 1.05 (0.72–1.55) 0.69 (0.42–1.13) 0.89 (0.65–1.22) 1.26 (0.81–1.95) 1.07 (0.68–1.68) 0.91 (0.61–1.35) 0.93 (0.69–1.26) 1.52 (1.07–2.15)* 0.77 (0.55–1.07) 0.96 (0.72–1.28) 1.30 (0.93–1.81) 0.80 (0.64–1.00)* 2.63 (2.03–3.41)* 0.98 (0.68–1.41) 2.14 (1.41–3.26)* 1.11 (0.81–1.53) 5.00 (2.94–8.52)* * 0.10 (0.05–0.17)* 0.53 (0.31–0.92)* Page 6 of 11 (page number not for citation purposes)