1. Partial Equilibrium Models
Partial equilibrium models only examine the market in which the tax is imposed and ignores other markets.
Most appropriate when the taxed commodity is small relative to the economy as a whole.

2. Partial Equilibrium Models: Per-unit Taxes
Unit taxes are levied as a fixed amount per unit of commodity sold
Federal tax on cigarettes, for example, is 39 cents per pack.
Assume perfect competition. Then the initial equilibrium is determined as (Q0, P0) in Figure 12.1.

3. Figure 12.1

4. Partial Equilibrium Models: Per-unit Taxes
Next, impose a per-unit tax of $u in this market.
Key insight: In the presence of a tax, the price paid by consumers and price received by producers differ.
Before, the supply-and-demand system was used to determine a single price; now, there is a separate price for each.

5. Partial Equilibrium Models: Per-unit Taxes
How does the tax affect the demand schedule?
Consider point a in Figure Pa is the maximum price consumers would pay for Qa.
The willingness-to-pay by demanders does NOT change when a tax is imposed on them. Instead, the demand curve as perceived by producers changes.
Producers perceive they could receive only (Pa–u) if they supplied Qa. That is, suppliers perceive that the demand curve shifts down to point b in Figure 12.1.

6. Partial Equilibrium Models: Per-unit Taxes
Performing this thought experiment for all quantities leads to a new, perceived demand curve shown in Figure 12.2.
This new demand curve, Dc’, is relevant for suppliers because it shows how much they receive for each unit sold.

7. Figure 12.2

8. Partial Equilibrium Models: Per-unit Taxes
Equilibrium now consists of a new quantity and two prices (one paid by demanders, and the other received by suppliers).
The supplier’s price (Pn) is determined by the new demand curve and the old supply curve.
The demander’s price Pg=Pn+u.
Quantity Q1 is obtained by either D(Pg) or S(Pn).

9. Partial Equilibrium Models: Per-unit Taxes
Tax revenue is equal to uQ1, or area kfhn in Figure 12.2.
The economic incidence of the tax is split between the demanders and suppliers
Price demanders face goes up from P0 to Pg, which (in this case) is less than the statutory tax, u.

10. Numerical Example
Suppose the market for champagne is characterized by the following supply and demand curves:

11. Numerical Example
If the government imposes a per-unit tax on demanders of $8 per unit, the tax creates a wedge between what demanders pay and suppliers get. Before the tax, we can rewrite the system as:

12. Numerical Example
After the tax, suppliers receive $8 less per pack than demanders pay. Therefore:

13. Numerical Example
Solving the initial system (before the tax) gives a price of P=20 and Q=60. Solving the system after the tax gives:

14. Numerical Example
In this case, the statutory incidence falls 100% on the demanders, but the economic incidence is 50% on demanders and 50% on suppliers:

15. Partial Equilibrium Models: Taxes on Suppliers versus Demanders
Incidence of a unit tax is independent of whether it is levied on consumers or producers.
If the tax were levied on producers, the supplier curve as perceived by consumers would shift upward.
This means that consumers perceive it is more expensive for the firms to provide any given quantity.
This is illustrated in Figure 12.3.

16. Figure 12.3

17. Partial Equilibrium Models: Taxes on Suppliers versus Demanders
In our previous numerical example, the tax on demanders led to the following relationship:
If we instead taxed suppliers, this relationship would instead be:

18. Partial Equilibrium Models: Taxes on Suppliers versus Demanders
Clearly, these equations are identical to each other. The same quantity and prices will emerge as before.
Implication: The statutory incidence of a tax tells us nothing about the economic incidence of it.
The tax wedge is defined as the difference between the price paid by consumers and the price received by producers.

19. Partial Equilibrium Models: Elasticities
Incidence of a unit tax depends on the elasticities of supply and demand.
In general, the more elastic the demand curve, the less of the tax is borne by consumers, ceteris paribus.
Elasticities provide a measure of an economic agent’s ability to “escape” the tax.
The more elastic the demand, the easier it is for consumers to turn to other products when the price goes up. Thus, suppliers must bear more of tax.

20. Partial Equilibrium Models: Elasticities
Figures 12.4 and 12.5 illustrate two extreme cases.
Figure 12.4 shows a perfectly inelastic supply curve
Figure 12.5 shows a perfectly elastic supply curve
In the first case, the price consumers pay does not change.
In the second case, the price consumers pay increases by the full amount of the tax.

21. Figure 12.4

22. Figure 12.5

23. Partial Equilibrium Models: Ad-valorem Tax
An ad-valorem tax is a tax with a rate given in proportion to the price.
A good example is the sales tax.
Graphical analysis is fairly similar to the case we had before.
Instead of moving the demand curve down by the same absolute amount for each quantity, move it down by the same proportion.

24. Partial Equilibrium Models: Ad-valorem Tax
Figure 12.7 shows an ad-valorem tax levied on demanders.
As with the per-unit tax, the demand curve as perceived by suppliers has changed, and the same analysis is used to find equilibrium quantity and prices.

25. Figure 12.7

26. Numerical Example
Returning to our previous example, with a per-unit tax on demanders the system was written as:

27. Numerical Example
Now, with an ad-valorem tax (τD), the system is written as:

28. Numerical Example
If the ad-valorem tax on demanders was 10%, then relationship between prices is:

29. Partial Equilibrium Models: Ad-valorem Tax
The payroll tax, which pays for Social Security and Medicare, is an ad-valorem tax on a factor of production – labor.
Statutory incidence is split evenly with a total of 15.3%.
The statutory distinction is irrelevant – the incidence is determined by the underlying elasticities of supply and demand.
Figure 12.8 shows the likely outcome on wages.

30. Figure 12.8

31. Partial Equilibrium Models: Competition
We can also loosen the assumption of perfect competition.
Figure 12.9 shows a monopolist before a per-unit tax is imposed.

32. Figure 12.9

33. Partial Equilibrium Models: Competition
After a per-unit tax is imposed in Figure , the “effective” demand curve shifts down, as does the “effective” marginal revenue curve.
Monopolists’ profits fall after the tax, even though it has market power.

34. Figure 12.10

35. Partial Equilibrium Models: Profits taxes
Firms can be taxed on economic profits, defined as the return to the owners of the firm in excess of the opportunity costs of the factors used in production.
For profit-maximizing firms, proportional profit taxes cannot be shifted.
Intuition: the same price-quantity combination that initially maximized profits initially still does. Output does not change.

36. General Equilibrium Models
Looking at one particular market may be insufficient when a sector is large enough relative to the economy as a whole.
General equilibrium analysis takes into account the ways in which various markets are interrelated.
Accounts for both inputs and output, and related commodities