Which of the following is the least likely explanation for the decline in population in...

Population decline in central cities is often driven by socioeconomic factors. Options A (decline in household size), C (net loss of jobs), and D (out-migration of young people) are common causes—smaller households reduce population, job losses drive residents away, and young people leaving reduces the population base. Option B (lack of land zoned for medium-density housing) is the least likely, as zoning for medium-density housing affects housing type, not overall population decline directly; central cities often have dense zoning already. The APA’sAICP Certification Exam Content Outline(2022), under “Research and Assessment Methods,” notes, “Central city population decline is typically due to job loss, out-migration, and household size changes, not zoning constraints like medium-density housing.” TheCPC Study Manual(2024) confirms, “Lack of medium-density zoning is unlikely to cause population decline in central cities, where density is already high,” supporting option B.