Law of demand and the demand curve
The demand curve (D) slopes downward from left to right, showing the inverse link between price and quantity demanded: ceteris paribus, a higher price means a lower quantity demanded. A demand schedule is the table of quantities demanded at each price. Two reasons: the substitution effect (a dearer good loses buyers to cheaper substitutes) and the income effect (a higher price cuts real purchasing power, so less is bought even if nominal income is unchanged).
Movement along vs shift of demand
A movement along the demand curve (a change in quantity demanded) is caused only by the good's own price: a price fall is an extension, a price rise a contraction. A shift of the whole curve is caused by a non-price determinant — income, prices of related goods, tastes, population, advertising or expectations. A rightward shift means more demanded at every price; a leftward shift means less demanded at every price.
Six non-price determinants of demand
Shift factors: income (a normal good's demand rises, an inferior good's falls); prices of related goods (a dearer substitute shifts demand right, a dearer complement shifts it left); tastes and fashion; population (size and structure); advertising; and expectations of future price. A change that favours the good shifts demand right; the reverse shifts it left. Each is a whole-curve shift, not a movement along.
Drawn from real examiner reports.
Movement along vs shift confusion
Saying the curve shifts when the good's own price changes — or calling a non-price change a movement along it — is a classic error. A price change gives an extension or contraction (a point moves along the existing curve). A change in income, tastes or a related price gives a shift of the whole curve. Diagram questions on income or a related price need a shift.
A recurring source of lost marks in diagram questions across multiple Paper 1 sittings (June 2024 Paper 1R, Q1(g)): candidates moved the equilibrium point along an unchanged demand curve rather than shifting the curve itself.
Label the new curve and equilibrium
In a demand-shift diagram, a correct rightward shift still loses marks if the new demand curve, the new equilibrium price and the new equilibrium quantity are not labelled. The mark scheme gives one mark for each labelled element (e.g. D2, Pe1, Qe1). A correct shift that is left unlabelled scores partial credit only.
June 2024 Paper 1R Q1(g): many candidates lost marks for unlabelled new curve and new equilibrium points. Examiner tip: label the new shift and the new equilibrium points to gain full marks.
Generic answers ignore the context
Listing several determinants of demand without analysing how one operates in the stated market earns only the lowest band. Stronger answers pick one or two factors, explain the mechanism fully (define, then link cause to effect), and apply them to the extract's data. A generic answer that fits any market cannot reach Level 3 or access AO3.
November 2024 Paper 1: generic lists of determinants without contextualised chains of reasoning limited candidates to Level 1 or Level 2 on Analyse and Assess questions.
Demand is not quantity demanded
When price alone falls, demand does not "increase" — it is quantity demanded that extends along the curve. Demand (the whole curve) changes only when a non-price determinant changes. Writing "demand rises" for a price fall is loose language that examiners penalise in both written and diagram answers.
Inferior good is not an unpopular good
An inferior good is one whose demand FALLS when income RISES (and rises when income falls), such as budget pasta — not a good that is disliked or low quality. A normal good's demand rises with income. Misreading "inferior" as "poor quality" leads to the wrong shift direction in a recession scenario.
Income is not the only shift factor
There are at least six non-price shift factors — income, prices of related goods, tastes, population, advertising and expectations. Answers that treat income as the sole determinant miss marks in Analyse and Assess questions, which reward selecting the most relevant factor for the market in the extract.
Define needs two conceptual parts
A two-mark define / "what is meant by" question gives one mark per conceptual part. Defining demand needs both: the quantity consumers are willing AND able to buy, and at a given price. An example, or restating the term, scores zero.
Draw the shift, then label five things
For a demand-shift diagram, label: both axes (Price, Quantity), the original curve D1, the new curve D2, the new equilibrium price and the new equilibrium quantity. A correct shift without these labels loses the labelling marks — add each label as you draw, not afterwards.
Explain wants a full chain
An Explain answer on a demand change should read as a chain: identify the determinant, state the direction of the shift, then the effect on equilibrium price and quantity. Stopping at "demand rises" gives knowledge but no analysis — carry it through to the market outcome.
Demand is the quantity of a good or service that consumers are willing and able to purchase at a given price over a given time period. Both conditions must be satisfied: willingness without ability (no money) is not demand; ability without willingness is not demand either.
A demand schedule lists the quantities demanded at each possible price. When plotted on a graph (price on the vertical axis, quantity on the horizontal axis), these points trace out the demand curve (D), which slopes downward from left to right.
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