Final answer:
An increase in the average length of annual vacation and a decrease in the retirement age generally cause the economy’s PPF to shift inward. In contrast, an increase in immigration causes the PPF to shift outward. The out-migration of skilled workers results in an inward shift of the PPF.
Step-by-step explanation:
The Production Possibility Frontier (PPF) represents the maximum possible output combinations of two goods or services an economy can achieve when all resources are fully and efficiently utilized. A change in the economy's resource base, technology, or rules will shift the PPF.
An increase in the average length of annual vacation would likely cause the PPF to shift inward, as it implies that workers are spending less time producing goods and services.
An increase in immigration generally leads to a shift in the PPF outward. This is because the supply of labor increases, leading to more potential production.
A decrease in the average retirement age would also likely cause the PPF to shift inward, since fewer workers would be active in the labor market.
The migration of skilled workers to other countries, often referred to as a 'brain drain,' would cause the PPF to shift inward due to the reduction in the skilled labor force available for production within the economy.