Summary
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A change in the quantity demanded means that the movement is along the
curve. A change in demand means that the demand curve has moved.
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Factors that shift demand are changes in income, prices of other goods,
population and consumer preferences.
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An increase in demand causes both price and quantity to increase.
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A decrease in demand causes both price and quantity to decrease.
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Factors that shift supply are the prices of other products, technology,
the number of firms in the market and the prices of inputs.
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An increase in supply causes quantity to increase and the price to decrease.
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A decrease in supply causes quantity to decrease and the price to increase.
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If supply and demand move in the same direction quantity moves in the
same direction but the effect on price is unknown.
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If supply and demand move in opposite directions then the price moves
in the same direction as demand but the effects on quantity is unknown.
