Identify the relevant population for the following research foci, and suggest the appropriate sampling design to investigate the issues, explaining why they are appropriate. Wherever necessary, identify the population frame as well.
a. A gun manufacturing firm would like to know the types of guns possessed by various age groups in Washington, D.C.
b. A hospital administrator wants to find out if the single parents working in the hospital have a higher rate of absenteeism than parents who are not single.
c. A researcher would like to assess the extent of pilferage in the materials storage warehouses of manufacturing firms on the East Coast.
d. The director of human resources wants to investigate the relationship between drug abuse and dysfunctional behavior of blue-collar workers in a particular plant.