Air pollution and birth outcomes, study components. researchers collected data to
examine the relationship between air pollutants and preterm births in southern california. during
the study air pollution levels were measured by air quality monitoring stations. specifically, levels
of carbon monoxide were recorded in parts per million, nitrogen dioxide and ozone in parts per
hundred million, and coarse particulate matter (pm10) in μg/m3. length of gestation data were
collected on 143,196 births between the years 1989 and 1993, and air pollution exposure during
gestation was calculated for each birth. the analysis suggested that increased ambient pm10 and,
to a lesser degree, co concentrations may be associated with the occurrence of preterm births.53
in this study, identify
(a) the cases,
(b) the variables and their types, and
(c) the main research question.