Final answer:
The population studied consists of all applicants for federal funding for psychosocial rehabilitation across the U.S., with the goal of determining the percentage of these applicants who are in poverty.
Step-by-step explanation:
The population being studied by the sociologist in question is all the applicants for federal funding intended to assist with the costs of psychosocial rehabilitation for children with developmental disorders across the United States.
The sociologist grouped the applications by state and then randomly selected applicants from each state to determine the percentage of applicants who are in poverty.
This method ensures that the sample is representative of the larger population and can provide credible insights into the economic statuses of the applicants.