Table 1

Characteristics of the study sample*

CharacteristicsECRHS IECRHS IIECRHS III
N (%) or mean (SD)N (%) or mean (SD)N (%) or mean (SD)
Symptomatic study arm544 (14.8)
Women1956 (53.3)
Age in years34.3 (7.1)43.0 (7.0)54.3 (7.1)
Height in cm170.6 (9.4)170.3 (9.4)169.4 (9.5)
Weight in kg69.5 (13.5)74.0 (15.1)77.9 (16.1)
BMI
 Continuous, in kg/m2 23.8 (3.7)25.4 (4.3)27.1 (4.9)
 Underweight453 (12.3)222 (6.1)119 (3.2)
 Normal weight2097 (57.1)1676 (45.8)1224 (33.3)
 Overweight892 (24.3)1298 (35.5)1481 (40.3)
 Obese231 (6.3)461 (12.6)849 (23.1)
Smoking status
 Non-smoker1651 (45.0)1576 (42.9)1518 (41.3)
 Ex-smoker818 (22.3)1119 (30.5)1500 (40.8)
 Current smoker1204 (32.8)978 (26.6)655 (17.8)
Secondhand smoke exposure, yes1939 (52.9)1321 (36.1)680 (18.6)
Current asthma, yes†378 (10.5)491 (13.8)570 (16.2)
Age completed full-time education
 <17 years675 (21.5)
 17–20 years1205 (38.4)
 >20 years1256 (40.1)
Physical activity. Active status‡1363 (52.2)
Any long-term limiting illness, yes§405 (17.1)
Lung function
 FVC (mL)4516 (988)4354 (980)3964 (948)
 FEV1 (mL)3702 (798)3485 (790)3006 (753)
 FEV1/FVC (%)82.3 (6.9)80.3 (6.5)75.8 (6.5)
Lung function (z-scores)¶
 FVC z-score0.01 (0.95)0.02 (1.00)−0.08 (0.94)
 FEV1 z-score−0.01 (1.06)−0.03 (1.08)−0.34 (1.04)
 FEV1/FVC z-score−0.06 (1.03)−0.10 (1.00)−0.48 (0.89)
  • *Some variables had missing values. Number of missing values for ECRHS I: 10 in secondhand smoke exposure, 78 in current asthma, and 537 in age completed full-time education. Number of missing values for ECRHS II: 18 in secondhand smoke exposure, 118 in current asthma, 1062 in physical activity and 1300 in any long-term limiting illness. Number of missing values for ECRHS III: 14 in secondhand smoke exposure and 163 in current asthma.

  • †Current asthma was defined as having reported physician-diagnosed asthma and at least one of the following: asthma-like symptoms (wheeze, nocturnal chest tightness, attacks of breathlessness after activity/at rest/at night-time), asthma attacks, use of inhaled/oral medicines for breathing problems (in the last 12 months), or current use of inhalers, aerosols or tablets for asthma.

  • ‡Individuals were categorised as being active if they exercised with a frequency of two or more times a week and with a duration of about 1 hour a week or more.

  • §The following illnesses were considered: hypertension, heart disease, diabetes, cancer or stroke.

  • ¶Lung function z-scores were derived using Global Lung Initiative 2012 equations.

  • BMI, body mass index; FEV1, volume expired in the first second; FVC, forced vital capacity.