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. Suppose the length of gestation data were collected on 142,126 births between the years 1989 and 1993, and air pollution exposure during gestation was calculated for each birth. (a) Identify the population of interest in this study. all births between 1989 and 1993 in the US all births in the US all births in Southern California all births between 1989 and 1993 in Southern California all births between 1989 and 1993 in California Identify the sample in this study. The sample consists of births in the population of interest. (b) Comment on whether or not the results of the study can be generalized to the population, and if the findings of the study can be used to establish causal relationships. If the births in this sample can be considered representative of all births in the population of interest, then the results generalizable to the entire population of interest. Additionally, since the study is , the findings be used to establish causal relationships