Inflation and the CPI: AP Macroeconomics Study Guide

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Where Inflation Sits in the AP Macro Course

Inflation and the CPI appear in the AP Macroeconomics unit on economic indicators and the business cycle, alongside GDP and unemployment. The course then uses the price level as one of the two axes of the aggregate demand and aggregate supply model, so every demand or supply shift you analyze later is partly an inflation question. Inflation returns as the vertical axis of the Phillips curve in the unit on the long-run consequences of stabilization policy, where you must distinguish the short-run trade-off from the vertical long-run curve at the natural rate of unemployment. It appears again in the financial sector unit through the Fisher equation and in the open economy unit through its effect on exchange rates and net exports.

The Calculations You Will Be Asked to Do

To build a price index, divide the cost of the fixed market basket in the current year by its cost in the base year and multiply by 100; the base year index equals 100 by construction. To find the inflation rate between two years, subtract the earlier index from the later one, divide by the earlier one, and multiply by 100. You should also be able to deflate a nominal value into real terms by dividing by the price index and multiplying by 100, and to apply the Fisher relationship: the real interest rate approximately equals the nominal rate minus the inflation rate, and the nominal rate approximately equals the real rate plus expected inflation. Watch the wording — expected inflation determines the nominal rate set in advance, while actual inflation determines the realized real rate.

Types, Costs, and Common Traps

Be able to classify inflation as demand-pull, shown as a rightward shift in aggregate demand, or cost-push, shown as a leftward shift in short-run aggregate supply and accompanied by falling output — the stagflation case. Know who gains and loses from unanticipated inflation: borrowers with fixed nominal rates gain at the expense of lenders, and savers holding cash and workers on fixed nominal contracts lose. Know the standard costs — menu costs, shoe-leather costs, and the distortion of price signals. Two traps recur: inflation is a rise in the general price level, not in one good's price, and disinflation (a falling inflation rate that is still positive) is not the same as deflation (a negative rate). Also remember the CPI uses a fixed basket while the GDP deflator covers everything produced domestically, so the two can diverge.

Key Terms to Know

Inflation vocabulary is unusually easy to half-know, and half-knowing it is exactly what free-response rubrics catch. Make sure you can state each of these precisely and, where a pair is involved, explain what distinguishes the two members of the pair — disinflation against deflation, headline against core, and demand-pull against cost-push are the three that separate strong answers from weak ones.