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By the end of this section, you will be able to:

  • Identify equilibrium price and quantity through the four-step process
  • Graph equilibrium price and quantity
  • Contrast shifts of demand or supply and movements along a demand or supply curve
  • Graph demand and supply curves, including equilibrium price and quantity, based on real-world examples

Let’s begin this discussion with a single economic event. It might be an event that affects demand, like a change in income, population, tastes, prices of substitutes or complements, or expectations about future prices. It might be an event that affects supply, like a change in natural conditions, input prices, or technology, or government policies that affect production. How does this economic event affect equilibrium price and quantity? We will analyze this question using a four-step process.

Step 1. Draw a demand and supply model before the economic change took place. To establish the model requires four standard pieces of information: The law of demand, which tells us the slope of the demand curve; the law of supply, which gives us the slope of the supply curve; the shift variables for demand; and the shift variables for supply. From this model, find the initial equilibrium values for price and quantity.

Step 2. Decide whether the economic change being analyzed affects demand or supply. In other words, does the event refer to something in the list of demand factors or supply factors?

Step 3. Decide whether the effect on demand or supply causes the curve to shift to the right or to the left, and sketch the new demand or supply curve on the diagram. In other words, does the event increase or decrease the amount consumers want to buy or producers want to sell?

Step 4. Identify the new equilibrium and then compare the original equilibrium price and quantity to the new equilibrium price and quantity.

Let’s consider one example that involves a shift in supply and one that involves a shift in demand. Then we will consider an example where both supply and demand shift.

Good weather for salmon fishing

In the summer of 2000, weather conditions were excellent for commercial salmon fishing off the California coast. Heavy rains meant higher than normal levels of water in the rivers, which helps the salmon to breed. Slightly cooler ocean temperatures stimulated the growth of plankton, the microscopic organisms at the bottom of the ocean food chain, providing everything in the ocean with a hearty food supply. The ocean stayed calm during fishing season, so commercial fishing operations did not lose many days to bad weather. How did these climate conditions affect the quantity and price of salmon? [link] illustrates the four-step approach, which is explained below, to work through this problem. [link] provides the information to work the problem as well.

Good weather for salmon fishing: the four-step process

The graph represents the four-step approach to determining shifts in the new equilibrium price and quantity in response to good weather for salmon fishing.
Unusually good weather leads to changes in the price and quantity of salmon.
Salmon fishing
Price per Pound Quantity Supplied in 1999 Quantity Supplied in 2000 Quantity Demanded
$2.00 80 400 840
$2.25 120 480 680
$2.50 160 550 550
$2.75 200 600 450
$3.00 230 640 350
$3.25 250 670 250
$3.50 270 700 200

Questions & Answers

what is net national income
Ibrahim Reply
relation between business economics and traditional economics
Netra Reply
more explanation on GDP
Isaac Reply
it is a country total out put of goods and services divided by the total population of the country.I think it can also be derived from the country labour force,,because it mostly depend on the labour force and the level of technology .
Tantoh
labour force and technological progress leads to greater production increases the GDP
Ahmed
what is elasticity of demand
Jessica
degree of responsiveness of demand to changes in price and other factors that influence demand.
OBIAJULUM
It is the degree of responsiveness of demand and supply to a little change in price of a goods and services
Ibrahim
What is economics?
Bubu Reply
by this time
Emmanuel
It is a social science that analyses production,distribution and consumption of goods and services
Emmanuel
A social science that study human behavior in relationship with decision making
Jessica
a social science that studies human behavior as a relationship between ends and scarce means which has alternative uses
Charllote
it is a science that study human begin as a relation to ends and scarce should which have alternative uses
Ibrahim
the science in which we study about the investement of our wealth.
Atteq
What are the typical patterns of GDP for a high-income economy like the United States in the long run and the short run?
mwangala Reply
What are the limitation and significant of macroeconomic
Usman Reply
explain the significance of concerpt of opportunity cost in planning
Mwanaid Reply
what is meant by the price elasticity of demand?
Martine Reply
when price of a commodity increase it's demand contracts , and whe the price of a commodity decreases it's demand expands so the degree of change in demand in response to change in own price of the commodity is called PED . Ed = percentage change in quantity demanded / percentage change in price
shaswat
What are the limitations of macroeconomic and their segnificant
Usman Reply
Discuss the role of competition in stimulating economic growth?
Daniel Reply
competition stimulate economic growth because in such types of economy,they is no monopoly power every supplier will want to produce to meet customers choice which brings about quality production and attract invested and customers into such economy
Koka
competition creates Monopoly because of economy of scale. it's not antithesis but different side of same coin
toko
competition result in high economic growth since every firm will intend to provide quality services and products to meet customers needs and requirements unlike in Monopoly situation where a firm just provide what it want to resulting in large stock piles of unwanted products ,ie inefficiency, howev
Mark
microeconomics study part of the economy but macroeconomic study the whole economy
Olokun Reply
studying the whole economy, solving the problem of the economy and building up the economy
Olokun
micro means small while macro means large
Olokun
standard of living is the footsteps of an economy because it plays important role for country to have crucial view about their budget ,import and export
Olokun
it will be differ because economic agent will only take their views on some part of household
Olokun
can opportunity cost be zero
OBED Reply
how many types of transportation do we have
Jacob
yes. when a customer's purchasing power is high, he may have d ability to purchase all he needs, dt makes opportunity cost zero
George
please can give more explanation on this question
OBED
what are the factors production
PETER Reply
Labour capital entrepreneurs
Leta
Land,capital, labour,and the entrepreneur
Tantoh
I will like to know use of calculus in economics
JHUMA Reply
do they use it in economics?
Pranav
I want to know if I should take calculus or statistics and probability my senior year of highschool
Yahir
yes for example in monopolistic competitive market..... TR=TC* & THIS CALCULATED BY CHANGING( DERIVATIVE LAW) MR =MC ** WILL BE THE FORMULA THAT USE.
Leta
please in which topic in economic is the question coming from.
Tantoh
from PCF in economics
Leta
why is unitary proportional to responsiveness
Etim Reply

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Source:  OpenStax, Principles of economics. OpenStax CNX. Sep 19, 2014 Download for free at http://legacy.cnx.org/content/col11613/1.11
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