Notes: Aggregate Demand and Supply — Transcript Concepts

Overview of Aggregate Demand and Supply (from Transcript)

• The transcript discusses shifts in the aggregate supply curve (AS) and aggregate demand (AD) in response to costs, currency movements, technology, and policy.
• Key goal: understand what moves AD, SRAS, and LRAS, and how the economy returns to its potential output (Y*).
• Important questions raised:
  • What happens when input costs fall or rise?
  • How do currency depreciation and imported inputs affect production costs and the curves?
  • How does technology affect potential output?
  • What mechanism returns the economy to potential output in the long run?
  • What role do menu costs and wage/prices rigidity play in price adjustments?

Key concepts and definitions

• AD (Aggregate Demand): total spending in the economy on goods and services at various price levels.

• SRAS (Short-Run Aggregate Supply): relationship between the price level and the quantity of goods/services firms are willing to supply in the short run, holding some inputs fixed.

• LRAS (Long-Run Aggregate Supply): the vertical, economy’s potential output Y* when all prices, including wages, have fully adjusted.

• Potential output: the maximum sustainable level of real GDP the economy can produce without increasing inflation, denoted as $Y^*$.

• Price level: denoted as $P$ (or $P_t$ over time).

• Menu costs: costs associated with changing posted prices (e.g., reprinting menus, updating catalogs, system updates).

• Wage rigidity: downward wage rigidity; wages tend not to fall easily due to contracts, norms, or negotiation frictions.

• Exchange rate effects: depreciation/appreciation of a currency affects the cost of imported inputs and capital goods.

• Core relationships (diagrams accompany these in typical courses):

  • AD curve is downward-sloping in the price level–real GDP space.
  • SRAS curve is upward-sloping: higher prices incentivize more output in the short run due to sticky input costs.
  • LRAS is vertical at $Y^*$, reflecting that in the long run real output is determined by the economy’s resources and technology, not by the price level.

• Fundamental equilibrium ideas:

  • Short-run equilibrium: intersection of AD and SRAS at some $Y<em>{SR}$ and $P</em>{SR}$.
  • Long-run adjustment: if AD or SRAS shifts, the economy moves away from $Y^<em>$ in the short run but tends to return to $Y^</em>$ over time as wages and other nominal/real prices adjust.

How input costs and currency movements shift the curves

• Cheaper production inputs

  • If something makes production cheaper (lower input costs or lower wages), SRAS shifts to the right (more output can be produced at each price level).
  • This is often described as a downward/ rightward shift in SRAS (output rises, price may fall or rise less).
  • Mechanism: lower costs reduce per-unit production costs, so firms supply more at each price.

• Currency depreciation and imported inputs

  • If the domestic currency weakens (depreciation), imported inputs and capital goods become more expensive.
  • Consequences:
  • Short-run effect: higher production costs shift SRAS to the left (or up in price terms), reducing output at each price level and increasing the price level (cost-push pressure).
  • The transcript notes that if capital goods become more expensive, aggregate demand effects may also arise via investment channels (AE ≈ Y), though the clean interpretation is that higher production costs push SRAS left.
  • Example from transcript: buying machines or inputs from abroad becomes costlier as the rand depreciates; higher costs feed into production and can reduce output or raise prices.

• Technological improvements and higher potential output

  • If technology improves (e.g., new tech allows drilling deeper, 5 km instead of 2 km), LRAS shifts to the right (Y* increases).
  • This reflects a higher capacity of the economy to produce goods/services at given prices in the long run.
  • The transcript uses this idea to illustrate a positive supply shock that raises potential output.

Government spending and short-run vs long-run dynamics

• Government spending increase (a fiscal policy impulse)

  • In the short run: higher G shifts AD to the right (AD → AD’). This raises equilibrium output and the price level (Y↑, P↑).
  • The transcript notes a scenario where “p2 is not greater than p1” and wages adjust upwards—this implies wage-price dynamics that can partially offset the initial boost via SRAS shifting left as wages and input costs adjust.
  • Conceptual takeaway: AD shocks move the economy in the short run; in the long run, price/wage adjustments restore output toward Y*.

• The long-run adjustment mechanism (return to potential output)

  • The central question: how do we get back to the potential level of output after a displacement?
  • Classical/long-run view: prices and wages adjust over time, shifting SRAS until the economy returns to Y* with the price level adjusting to clear markets.
  • In the explicit framework: after an AD or SRAS shock, the market forces (price and wage adjustments, expectations) move the economy along toward the vertical LRAS at Y*.
  • The transcript prompts the idea that the “mechanism behind getting back there” involves adjustments in wages and other input prices, and the long-run equilibrium occurs where AD intersects LRAS with Y = Y*.

Price-setting, menu costs, and wage dynamics

• Menu costs and price changes

  • Changing prices can be costly due to menu costs (updating menus, catalogs, software, prices in menus). This can cause prices to be sticky in the short run.
  • When menu costs are high, firms may delay price changes even if demand shifts, slowing the adjustment of the economy to shocks.
  • Digital technologies and reduced menu costs make price adjustments cheaper, enabling faster responses to shocks.

• Why prices won’t go down through wages (and related implications)

  • Intuition: If a firm wants to lower its price, it would reduce profits. To sustain profitability without lowering prices, firms would need to reduce costs.
  • However, downward wage adjustments are often difficult due to contracts, norms, and coordination frictions; wages are relatively sticky downward.
  • Practical implication: price declines via wage cuts are limited; instead, price decreases may occur only if costs fall (e.g., lower input costs) or if prices adjust via other channels, meaning prices may not fall easily through wage reductions alone.
  • The transcript uses this to explain why in many economies prices are sticky downward and why inflation dynamics can be persistent.

Mathematical summaries and relations (LaTeX)

• Aggregate demand identity (simple Keynesian view)
  • $AD = C + I + G + NX$
  • In equilibrium (short run), the economy balances where $AD = SRAS$ at some combination of $Y<em>{SR}$ and $P</em>{SR}$.
• Long-run equilibrium
  • Long-run supply is vertical: $LRAS: Y = Y^*$
  • In the long run, the price level adjusts to clear the AD/AS framework, bringing real GDP back to potential output: $Y = Y^<em>$ with price level at some $P^</em>$ such that $AD(P^<em>, Y^</em>) = SRAS(P^<em>, Y^</em>)$ in the long-run sense (conceptually, SRAS becomes LRAS as expectations adjust).
• Shifts and effects (summary equations)
  • Lower input costs → SRAS shifts right: $SRAS o SRAS'$ with $Y_{SR}↑$ at given P, or lower P for a given Y.
  • Higher input costs due to depreciation → SRAS shifts left: $SRAS o SRAS''$ with $Y_{SR}↓$ at given P, or higher P for a given Y.
  • Technological progress → LRAS shifts right: $LRAS o LRAS'$ with $Y^<em><em>{ ext{new}} > Y^</em></em>{ ext{old}}.$
• Conceptual summary of adjustment mechanism
  • Short-run: shocks move the economy away from Y*; AD and SRAS determine new (Y, P).
  • Long-run: wages/price adjustments (and sometimes expectations) shift SRAS toward LRAS, restoring Y to Y*; the price level is the vehicle by which this adjustment occurs.

Connections to prior concepts and real-world relevance

• Relation to fiscal policy
  • Government spending changes shift AD and can be used to stabilize output in the short run, with trade-offs in the price level.
• Relation to currency regimes and openness
  • Open economy effects: currency depreciation changes import costs, affecting SRAS; depreciation can also affect net exports (NX), which feeds back into AD.
• Technology and growth
  • Technological improvements alter the economy’s production possibilities, shifting LRAS and enabling higher sustainable GDP over time.
• Menu costs and price dynamics in the real world
  • Firms facing high menu costs will adjust prices slowly, contributing to price stickiness, slower inflation dynamics, and longer persistence of shocks.
• Wages as a source of rigidity
  • Downward wage rigidity can slow the self-correcting adjustment, particularly after negative demand shocks; price adjustments may be the primary channel for returning toward Y* in the short run, with wages catching up over time.

Practical takeaways for exam-style understanding

• A fall in production costs shifts SRAS to the right (increase in real output, possible lower price level). A rise in input costs shifts SRAS to the left (lower output, higher price level).
• A depreciation of the domestic currency increases the cost of imported inputs, shifting SRAS left and potentially lowering output or raising the price level.
• Technological progress that expands productive capacity shifts LRAS to the right (higher potential output).
• An increase in government spending shifts AD to the right in the short run, raising both output and the price level; long-run effects depend on how wages and prices adjust.
• Menu costs induce price rigidity, slowing the adjustment of prices to shocks; reductions in menu costs (e.g., via digital pricing) can speed up adjustment.
• Downward wage rigidity can slow the decrease of prices via wage cuts; firms may need to rely on cost reductions or demand-driven price changes to adjust.
• The economy tends to return to potential output over time through adjustments in wages and other prices, moving SRAS and AD toward the long-run equilibrium where Y = Y^*.