2.3. Sample Size Calculation. Sample size calculation was
done with a type I error of 5% and a study power of 80%. In
the absence of baseline data, the exposure of healthy Lebanese
residents to pollution was considered to be equal to 50%. The
minimal sample size necessary to show a twofold increase
in risk of cardiovascular diseases consisted of 330 subjects,
divided into 111 cases and 222 controls. In the present study
the simple size was 340 divided into 121 cases and 219 controls.
Smoking status was also assessed for cigarette and water pipe
smoking separately. Due to the small number of previous
cigarette smokers, this subgroup was combined with current
smokers. Passive smoking at home and at work was also
weighed. On the subject of pollution, the traffic exposure
indicator was assessed by the following question: “Are you
living near a busy highway (100 meters)?”
The diesel emission exposure indicator was evaluated by
the following question: “Are you living close to local diesel
generator”? Traditional cardiovascular risk factors (CVRFs)
were also collected from the hospital charts: hypertension,
triglyceride, HDL (high density lipoprotein concentration),
LDL (low density lipoprotein concentration), family history
of cardiovascular disease (CVD), and obesity according
to Body Mass Index scale (BMI) “normal weight” (BMI
18.5–24.9 kg/m2
), “overweight” (BMI 25.0–29.9 kg/m2
), and
“obese” (BMI ≥ 30 kg/m2
) [24].