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Table 1 Characteristics of the study participants

From: Inhalable particulate matter and mitochondrial DNA copy number in highly exposed individuals in Beijing, China: a repeated-measure study

  Office workers Truck drivers p-value a
  (n=60) (n=60)  
Age [years], mean ± SD 30.27 ± 7.96 33.53 ± 5.65 0.01
Sex, n (%)    
      Male 40 (66.67) 40 (66.67)  
      Female 20 (33.33) 20 (33.33) 1.00
BMI [kg/m 2 ], mean ± SD 22.76 ± 3.38 24.27 ± 3.21 0.01
Smoking, n (%)    
      Never smoker 35 (58.33) 34 (56.67)  
      Former 2 (3.33) 2 (3.33)  
      Current 23 (38.33) 24 (40) 1.00
Pack-years of smoking, mean ± SD b 1.2 ± 2.7 5.1 ± 9.3 0.003
Work hours per week, mean ± SD 50.6 ± 11.0 67.3 ± 14.0 <0.001
Day of the week on the two study days, n (%)    
      Monday 16 (13.33) 19 (15.83)  
      Tuesday 18 (15) 13 (10.83)  
      Wednesday 14 (11.67) 15 (12.5)  
      Thursday 15 (12.5) 20 (16.67)  
      Friday 17 (14.17) 19 (15.83)  
      Saturday 18 (15) 16 (13.33)  
      Sunday 22 (18.33) 18 (15) 0.88c
Average temperature on the two study days, mean ± SD 25.36 ± 2.51 25.34 ± 2.51 0.96c
Average dew point on the two study days, mean ± SD 20.63 ± 2.06 20.61 ± 2.13 0.93c
  1. a P-values were calculated using Student’s t-test and Fisher’s exact test for continuous and categorical variables, respectively.
  2. b Only current or former smokers.
  3. c Cumulative over the two study days. Based on 240 total observations (120 study days for office workers and 120 study days for truck drivers). P-values were obtained from mixed-effects regression models.