Demand and Supply: Determinants, Shifts, and Production Interactions

Demand and the Demand Function

  • The demand relation describes the direct link between the price of a good and the quantity that consumers are willing to purchase.
  • Graphically, the setup uses the price on the vertical axis and the quantity demanded on the horizontal axis. The demand function is written as a function of price, with the quantity demanded being the output: q_d = f(p). In full generality, the quantity demanded depends on more than price:
    • The price of the good (p)
    • Other determinants (non-price factors) such as consumer income, prices of related goods, tastes/preferences, expectations about future prices, and the asset characteristics of the good.
  • Notation: the quantity demanded is often written as q_d = f(p, ext{other determinants}). Conceptually this is like y = f(x) or fx = g(y); the argument to the function is the price (and other inputs).
  • The demand function for a specific good (example: motorcycles) depends on many variables beyond price, including:
    • Income of consumers
    • Prices of related goods, including substitutes and complements
    • Consumer preferences or tastes
    • Expectations about future prices
    • Product characteristics (e.g., horsepower of a motorcycle)
  • The non-price determinants shift the entire demand curve (not just move along it):
    • Changes in income shift demand (for normal vs inferior goods)
    • Changes in the prices of substitutes or complements shift demand
    • Changes in tastes/preferences or in expectations shift demand
    • Changes in other product attributes (e.g., motorcycle horsepower, safety features) affect demand through preferences
  • Example: motorcycles
    • Substitute example: ebikes
    • Complement example: helmet, protective gear (cost of obtaining satisfaction increases if these go up)
    • Aesthetic or technical attributes (e.g., horsepower) affect preferences within the demand for a given motorcycle class (e.g., 1000 cc bike)
    • A movie star’s riding on a big bike could shift preferences and increase demand for certain motorcycles
  • The determinants of demand (non-price factors) include: income, prices of related goods (substitutes and complements), tastes, expectations about future prices, and attributes of the good (e.g., horsepower).
  • Relationship intuition:
    • If a substitute’s price rises, demand for the motorcycle increases (shifts right).
    • If a complement’s price rises, demand for the motorcycle decreases (shifts left).
    • If consumer income rises and the motorcycle is a normal good, demand shifts right; if it is an inferior good, demand shifts left with higher income.
  • Normal vs inferior goods:
    • Normal goods: demand increases with income (shift right when income rises).
    • Inferior goods: demand decreases with income (shift left when income rises).
    • Example hints from the transcript: motorcycles are treated as a normal good; craft dinner / generic KD is treated as an inferior good; potatoes are discussed as an inexpensive staple that might be considered inferior relative to higher-quality foods as income rises.
  • Related goods in demand:
    • Substitutes: two goods that can replace each other in consumption (e.g., motorcycles and ebikes).
    • Complementary goods: goods that are often consumed together (e.g., a motorcycle and helmet).
    • If the price of a substitute goes up, the quantity demanded for the motorcycle increases (demand shifts right).
    • If the price of a complement goes up, the quantity demanded for the motorcycle decreases (demand shifts left).
  • Summary intuition: Demand shifts when non-price determinants change because the value or utility of the good, or the available alternatives, changes for consumers.
  • Qualitative focus vs quantitative math: The lecture emphasizes qualitative understanding of how determinants shift demand, with later steps introducing the math of equilibrium. The current discussion is descriptive and conceptual, not computational.

The Demand Function: Formal Representations

  • General form: the quantity demanded is a function of price and other determinants. A compact representation is:
    • qd = f(p, I, Ps, P_c, T, E, H)
      where:
    • $p$ = price of the good
    • $I$ = income of consumers
    • $P_s$ = price of substitutes
    • $P_c$ = price of complements
    • $T$ = tastes/preferences
    • $E$ = expectations about future prices
    • $H$ = product characteristics (e.g., horsepower)
  • More general notation can also be written as a function of multiple inputs: q_d = f(p, ext{income}, ext{prices of related goods}, ext{preferences}, ext{ expectations}, ext{attributes})
  • The key idea remains: demand is the quantity buyers want to purchase, given price and all other determinants, and non-price determinants shift the demand curve.

Demand Shifts: Determinants and Directions

  • Income effects:
    • Normal goods: income ↑ → demand shifts right (more quantity demanded at every price).
    • Inferior goods: income ↑ → demand shifts left (less quantity demanded at every price).
  • Prices of related goods:
    • Substitutes: if the price of a substitute rises, demand for the good increases (shift right).
    • Complements: if the price of a complement rises, demand for the good falls (shift left).
  • Tastes and preferences:
    • Positive changes in tastes or new information can increase demand (shift right).
    • Fashion, trends, or media influence (e.g., star riding a big bike) can shift demand.
  • Expectations about future prices:
    • If buyers expect prices to rise in the future, they may buy more today (demand shifts right).
  • Product attributes (characteristics):
    • Changes in horsepower, safety features, or other attributes can influence demand through preferences.
  • The example scenario described in the transcript:
    • For motorcycles, an increase in income is likely to increase demand (normal good).
    • A potential film or star influence can shift preferences and raise demand for a class of motorcycles (shift right).
    • The discussion of a thousand-cc bike highlights how consumer preferences can shift with perceived quality, status, or performance.
  • Practical intuition about shifts:
    • When non-price determinants increase demand, the entire demand curve shifts to the right.
    • When non-price determinants decrease demand, the entire demand curve shifts to the left.

Demand, Equilibrium, and the Role of Supply (Qualitative Preview)

  • Equilibrium in a market requires both demand and supply:
    • Demand: how much buyers want at each price
    • Supply: how much sellers are willing to offer at each price
  • The lecture notes that while shifts in demand are intuitive to analyze, the actual equilibrium price and quantity after a shift depend on the supply curve as well. Without the supply curve, you cannot determine the new equilibrium.
  • The next steps (to be covered in future sessions) will introduce the supply side and equilibria, focusing first on demand then on how shifts interact with supply to determine new equilibrium prices and quantities.

The Supply Curve and the Factors of Production

  • Definition: The supply function shows the relationship between the price of a good and the quantity firms are willing to produce and sell.
  • Graphical shape: The supply curve is typically upward sloping (quantity supplied increases as price increases); unlike demand, it is almost always downward-sloping in price when holding other determinants constant.
  • Exceptions: In some contexts, supply can be vertical or horizontal, but it is not downward sloping in the standard analysis.
  • Key terms:
    • Inputs (factors of production): labor, capital (machinery), land, and raw materials used to produce goods.
    • Inputs are costs that affect production decisions.
  • How input prices affect supply:
    • If input prices rise (e.g., wages rise), supply tends to decrease; the supply curve shifts to the left.
    • If input prices fall, supply tends to increase; the supply curve shifts to the right.
  • Technology and productivity:
    • Advances in technology increase productivity of inputs, shifting supply to the right (more output can be produced at the same price).
  • Substitutes and complements in production (production-side determinants):
    • Substitutes in production: Two different goods that could be produced with the same inputs. If the price of one goes up, producers shift resources to produce more of that good, reducing the supply of the other good.
    • Example: barley and wheat produced on the same land. If the price of barley rises, supply of barley increases while supply of wheat decreases (as resources shift toward barley).
    • Complements in production: Goods that are produced together from the same inputs. If the price of one by-product rises, producers increase output of the other product as well.
    • Example: cattle produce beef and leather; leather is a by-product. If the price of leather rises, beef supply may increase because producers shift to maximize total revenue from both outputs.
    • Oil and natural gas: Produced together; if the price of natural gas rises, oil production may increase as a complementary by-product increases in value.
  • Relationship recap for supply shifts:
    • Increase in input prices → supply shifts left (less supply at every price).
    • Technological progress → supply shifts right (more supply at every price).
    • Substitutes in production: price increase for one product can reduce the supply of the other and vice versa (direction depends on relative prices).
    • Complements in production: higher price for a by-product can increase the supply of the other product (and vice versa).
  • Intuition: Supply shifts reflect how easily and cheaply producers can produce output; higher costs or less productivity reduce supply, while lower costs or higher productivity increase supply.

Substitutes and Complements in Production

  • Substitutes in production (production-side):
    • When two goods use the same inputs, a higher price for one good makes producers allocate more resources to that good, reducing the supply of the other good.
    • Example from the transcript: If barley’s price goes up, barley supply increases and wheat supply decreases (holding other factors constant).
  • Complements in production (by-products):
    • Some goods are produced together; an increase in the price of one by-product can incentivize production that increases the supply of the other product.
    • Example: Leather and beef from cattle; if leather price is high, beef production (supply) may rise because both outputs are obtained from the same inputs.
  • Reservoir example: crude oil and natural gas produced together; a rise in the price of natural gas can lead to higher overall production, increasing the supply of both outputs.

Practical Takeaways and Exam-ready Points

  • Know the directions of shifts:
    • Demand: Right shift means higher quantity demanded at every price; Left shift means lower quantity demanded at every price.
    • Supply: Right shift means higher quantity supplied at every price; Left shift means lower quantity supplied at every price.
  • Determinants to memorize:
    • Demand: income (normal vs inferior goods), prices of substitutes and complements, tastes, expectations, and product attributes.
    • Supply: input prices, technology, prices of related goods in production (substitutes and complements in production).
  • Equilibrium concept: The equilibrium price and quantity are found at the intersection of the demand and supply curves. If either curve shifts, the equilibrium price and quantity will change; the exact new equilibrium depends on both curves and their relative shifts.
  • The qualitative emphasis in this portion of the course: Understanding how shifts occur and their directional effects is the foundation before solving the algebra for equilibrium in later units.
  • Real-world relevance: These concepts explain how policy changes (taxes, subsidies), income changes, price changes in related goods, fashion trends, safety regulations (helmet requirements), and technological progress can affect what people buy and what firms produce.
  • Ethical and practical implications: Regulations that alter prices or costs (e.g., safety equipment costs) may shift demand or supply in meaningful ways. Understanding these shifts helps in assessing welfare implications for consumers and producers.
  • Connection to prior and future lectures:
    • This note builds on the idea that demand and supply are shapes that respond to determinants beyond price.
    • The next steps will introduce mathematical analysis of equilibrium and how to quantify the effects of shifts on price and quantity with both curves present.

Quick Reference Formulas (LaTeX)

  • Demand function (general):
    qd = f(p, I, Ps, P_c, T, E, H)
  • Alternative compact demand representation:
    q_d = f(p, ext{income}, ext{prices of related goods}, ext{preferences}, ext{expectations}, ext{attributes})
  • Supply function (general):
    q_s = g(p, ext{input prices}, ext{technology}, ext{prices of related goods in production})
  • Market equilibrium condition (no surplus or shortage):
    qd(p^) = qs(p^)
  • Directional shift rules (conceptual):
    • If determinant increases demand, the demand curve shifts to the right: D  right.
    • If determinant decreases demand, the demand curve shifts to the left: D  left.
    • If determinant increases supply (e.g., technology), the supply curve shifts to the right: S  right.
    • If determinant decreases supply (e.g., higher input costs), the supply curve shifts to the left: S  left.