I am working with the 1-year ACS and attahced several characteristics of mother and father. These variables have an important number of missing values. What is the universe for characteristics of mother and father? Is there any other variable that determine if an observation includes mother and father characteristics? My sample is defined in part by age (16-24) and I would like to include in my analisys the EDUC_MOM and EDUC_POP but I want to be sure what are the observations I am not considering becuase the missing values of these two variables. Also, the missing values for any mother’s variable correspond to exactly the same individuals. Same happends with father’s variables.