AP Syllabus focus: ‘A positive or negative AD shock changes output, employment, and the price level in the same direction in the short run.’
Aggregate demand (AD) shocks are a core driver of short-run business cycle fluctuations. Using the AD-AS model, you should be able to predict how real GDP, employment, and the price level respond when AD shifts.
What an AD shock is in the AD-AS model
An AD shock is an unexpected change that shifts the AD curve right or left, changing overall planned spending at each price level.
These panels show the aggregate demand curve shifting due to changes in autonomous spending. An increase in aggregate demand shifts AD rightward (higher spending at every price level), while a decrease shifts AD leftward. This is the graphical definition of an AD shock: a redraw of the entire AD curve, not a point-to-point slide along a fixed AD curve. Source
AD shock: A shift in aggregate demand (rightward or leftward) that changes short-run equilibrium real output and the price level.
In the short run, wages and some input prices are slow to adjust, so firms respond to changes in demand by changing production rather than instantly changing all prices and wages.
How an AD shock changes short-run equilibrium
Starting point: short-run equilibrium
Short-run equilibrium is where the economy’s AD curve intersects SRAS, determining the current price level and real GDP.
Short-run equilibrium (AD-AS): The intersection of AD and SRAS, where total output demanded equals total output supplied at a particular price level.
After an AD shock, the economy moves to a new intersection of AD and SRAS.
This figure illustrates how an aggregate demand shift changes short-run equilibrium in the AD–AS model. A rightward shift of AD raises both the price level and real GDP at the new intersection with SRAS, while a leftward shift lowers both. The vertical LRAS line helps emphasize that these are short-run movements around potential output rather than a change in potential GDP itself. Source
Because SRAS is upward sloping, this movement changes real output, the price level, and therefore employment.
Positive AD shock (AD shifts right)
A positive AD shock shifts AD rightward (from AD₁ to AD₂). In the short run:
Real GDP increases (movement to a higher quantity of output on SRAS)
Price level increases (higher overall demand bids up prices)
Employment increases and unemployment falls (firms hire more labor to expand output)
Key intuition: with many wages/input costs temporarily sticky, higher demand raises firms’ revenues relative to costs, so producing more is profitable.
Negative AD shock (AD shifts left)
A negative AD shock shifts AD leftward (from AD₁ to AD₂). In the short run:
Real GDP decreases
Price level decreases
Employment decreases and unemployment rises
Key intuition: falling demand reduces firms’ sales; with sticky wages and contracts, firms cut production and labor hours/positions rather than instantly cutting all costs.
“Same direction” is the headline rule for AD shocks
For AD shocks in the short run, the model predicts that:
Real GDP and the price level move in the same direction
Employment moves with real GDP (so unemployment moves in the opposite direction of GDP)
This “same direction” pattern is the signature of demand-driven fluctuations in the AD-AS framework:
AD right → higher and higher
AD left → lower and lower
Avoiding a common mistake: shift vs. movement along AD
An AD shock is a shift of the AD curve, not a movement along it.
Movement along AD: caused by a change in the price level (quantity of output demanded changes)
Shift in AD (shock): caused by changes in overall spending behavior that are not triggered by the current price level
In the short run analysis of shocks, you hold SRAS fixed and focus on how the new AD position changes the economy’s equilibrium outcomes.
FAQ
Yes. A flatter SRAS implies a larger change in $Y$ and a smaller change in $P$ for a given AD shift; a steeper SRAS implies the opposite.
Labour intensity and flexibility differ by sector. Industries with variable hours, temporary staffing, or flexible production can adjust employment more quickly than capital-intensive sectors.
Differences in spare capacity, wage rigidity, market competition, and how quickly firms adjust prices can change how much of the shock shows up as higher $P$ versus higher $Y$.
Examples include abrupt changes in consumer confidence, financial market stress that restricts borrowing, rapid shifts in foreign demand for exports, or sudden changes in government purchasing plans.
Firms may initially reduce overtime, cut hours, freeze hiring, or keep workers (“labour hoarding”) before layoffs appear in unemployment statistics, creating a timing gap.
Practice Questions
(2 marks) In the short run, what happens to the price level and real output after a positive aggregate demand shock?
Price level increases (1)
Real output increases (1)
(6 marks) Using the AD-AS model, explain the short-run effects of a negative aggregate demand shock on real GDP, the price level, and unemployment.
States AD shifts left (1)
Explains new short-run equilibrium occurs at AD–SRAS intersection (1)
Real GDP falls (1)
Price level falls (1)
Unemployment rises / employment falls (1)
Explicitly links “same direction” for and under AD shocks (1)
