We have learned that when only demand or supply shift, we can predict the direction of change in both equilibrium price and equilibrium quantity. But if both change, we can only confidently predict the direction of change for one of these; the other will always be indeterminate.

    The same logic can be used in reverse. For example, if we observe the equilibrium price and the equilibrium quantity both increasing, we look for factors that cause demand to increase. If we find that the equilibrium quantity is rising rapidly but price is remaining relatively unchanged, we look for two factors, one that causes demand to increase and one that causes supply to increase.

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