Notes: Opportunity Cost, Cost-Benefit Analysis, PPF, and Marginal Principle

Opportunity Cost and Cost-Benefit Thinking

  • General Idea: Economic decisions involve comparing benefits to costs. If benefits exceed costs, proceed. For mutually exclusive options, compare their economic surpluses.

  • Economic Surplus (SS): The total benefit (BB) of an option minus its opportunity cost (OCOC). S=B−OCS = B - OC

  • Opportunity Cost (OC): The true cost of choosing an option; it is the value of the next best alternative that must be forgone.

    • Includes more than just money (e.g., time, foregone benefits).

    • Sunk costs (past, unrecoverable expenditures) should be ignored in current decisions.

    • In economics, "cost" often implies opportunity cost, unlike in accounting where it usually means direct costs.

  • Decision Rule: Choose the option with the highest positive economic surplus. For two mutually exclusive options A and B:

    • OCAOC_A = Value of B (the next best alternative).

    • OCBOC_B = Value of A (the next best alternative).

Production Possibilities Frontier (PPF)

  • Core Idea: Scarcity necessitates trade-offs. The PPF visualizes the maximum feasible combinations of two goods or activities, given limited resources.

  • Example: Spending study time on Economics vs. Psychology.

    • Endpoints: Show maximum possible output if all resources are dedicated to one good (e.g., (0, 24) for Economics points if all time is on Economics, (12, 0) for Psychology points if all time is on Psychology).

  • Key Terms:

    • Efficient Outcome: Any point on the PPF, where resources are fully utilized.

    • Feasible but Inefficient: A point inside the frontier; attainable but not using resources fully.

    • Unattainable: A point outside the frontier, not possible with current resources.

  • Shifts of the Frontier:

    • Outward Shift: Occurs due to productivity gains (e.g., technology, learning) or increased resources (e.g., more time, capital). This expands the possible combinations.

    • Inward Shift: Due to a decrease in productivity or resources.

Marginal Principle

  • Core Idea: Many decisions can be broken into a sequence of smaller, incremental (marginal) steps. Decisions are made by comparing marginal benefits to marginal costs.

  • Marginal Cost (MC): The cost of producing or consuming one additional unit.

  • Marginal Benefit (MB): The benefit gained from producing or consuming one additional unit.

  • Rational Rule: Continue an activity as long as the marginal benefit of the next unit is at least as large as the marginal cost (MBextextgreater=MCMB ext{ extgreater= } MC). Stop when MB < MC. The optimal point is where MB=MCMB = MC (or as close as possible).

  • Example (Coffee):

    • If the MB of the 1st cup is $8 and MC is $3, buy.

    • If the MB of the 2nd cup is $6 and MC is $3, buy.

    • If the MB of the 3rd cup is $4 and MC is $3, buy.

    • If the MB of the 4th cup is $2 and MC is $3, do not buy.

    • Conclusion: Buy 3 cups to maximize total surplus.

  • Importance: The marginal rule is crucial for maximizing total