Money Market graph mistakes

15 ways students lose points on this diagram, each taken from a worked free-response scenario. Every entry names the reasoning that causes the error, not just the error, because the wrong answer is usually a sensible thought applied to the wrong curve.

1. 01

   Central Bank Bond Purchase

   The mistake. The most common wrong answer is shifting MS to the LEFT, because students hear "the central bank is buying" and picture the bank taking money in. The bank pays for those bonds with newly created reserves, so money flows out to banks and the public, which is an expansion of the money supply.

   Draw this instead. Money supply (MS) shifts right.

   Exam tip. On any open-market operation, ask which side of the trade the central bank is on and where the money ends up: the bank buys bonds and pays out new money, so MS shifts right.

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2. 02

   Reserve Requirement Change

   The mistake. Many students shift MD left instead, reasoning that "banks are now required to hold more money." A reserve requirement limits how much money the banking system can create, which is the quantity in existence, not how much money households and firms want to hold at each interest rate.

   Draw this instead. Money supply (MS) shifts left.

   Exam tip. The reserve requirement, the discount rate, and open-market operations are all central bank tools, so every one of them moves MS and none of them moves MD.

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3. 03

   Nominal GDP and Transactions

   The mistake. The frequent error is shifting MS right, on the logic that a bigger economy "has more money circulating." The quantity of money in existence is set by the central bank, which the stem says did nothing; a larger volume of transactions changes only how much money people want to hold, so the adjustment happens through a higher interest rate.

   Draw this instead. Money demand (MD) shifts right.

   Exam tip. When a stem changes the price level or income and explicitly says the central bank takes no action, the answer is always MD alone, with the interest rate moving in the same direction as MD.

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4. 04

   Discount Rate Cut

   The mistake. A large share of students move nothing at all and simply slide down the MD curve, treating the discount rate as if it were the interest rate on the vertical axis. The discount rate is an administered rate that is not plotted on this graph; the rate on the axis is the equilibrium market rate, and it falls only because MS shifted right first.

   Draw this instead. Money supply (MS) shifts right.

   Exam tip. Never equate a policy rate named in the stem with the rate on the y-axis: the tool shifts a curve, and the equilibrium rate you read off the graph is the result of that shift, never the cause.

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5. 05

   Falling Price Level

   The mistake. Students often shift MS left because falling prices and a downturn sound contractionary. Nothing here changed the quantity of money the central bank supplies; a lower price level changes only how many dollars each purchase takes, which is a money demand determinant.

   Draw this instead. Money demand (MD) shifts left.

   Exam tip. The price level and money demand always move together: PL up shifts MD right, PL down shifts MD left, and the equilibrium interest rate follows MD in the same direction.

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6. 06

   Rise of Digital Payments

   The mistake. The typical wrong answer is shifting MS left, on the reasoning that "people are holding less money, so there is less money." The quantity of money in existence has not changed by a single dollar; only the amount people wish to hold at each interest rate has fallen, and the rate drops until they are willing to hold the same fixed quantity.

   Draw this instead. Money demand (MD) shifts left.

   Exam tip. Any innovation that lets people make the same purchases with smaller money balances, such as credit cards, ATMs, or payment apps, shifts MD left and leaves MS exactly where it was.

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7. 07

   Central Bank Bond Sale

   The mistake. The error students actually make here is shifting MD left, reasoning that "people handed over money to buy the bonds, so they demand less money." Handing money to the central bank removes it from circulation, which is a change in the quantity supplied; the willingness of households and firms to hold money at each interest rate is untouched.

   Draw this instead. Money supply (MS) shifts left.

   Exam tip. Sort every open-market operation by who ends up holding the money: the central bank selling bonds collects money and pulls it out of circulation, so MS shifts left and the interest rate rises.

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8. 08

   Lower Reserve Ratio

   The mistake. Students shift MS left here because the stem says something is being reduced and they map the word onto a leftward shift. What got smaller is the fraction of each deposit banks must hold idle, and a smaller required ratio means a larger multiplier and more deposit creation, so the money supply grows.

   Draw this instead. Money supply (MS) shifts right.

   Exam tip. Run every reserve-ratio stem through the multiplier, one divided by the required reserve ratio: a smaller ratio means a bigger multiplier, more deposit creation, and MS shifting right.

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9. 09

   Banks Hoard Reserves

   The mistake. The wrong answer students give here is "nothing shifts, because only the central bank can move MS," since the stem says no policy tool was used. The central bank supplies reserves, but banks' lending decisions determine how much deposit money is created from those reserves, so hoarding excess reserves shrinks the money supply even with every policy setting untouched.

   Draw this instead. Money supply (MS) shifts left.

   Exam tip. Excess reserves are the classic leak in the money multiplier: when a stem says banks choose to sit on reserves rather than lend, shift MS left even though the central bank did nothing.

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10. 10

    Merchants Stop Taking Cards

    The mistake. The specific wrong answer is shifting MS right, on the reasoning that "more currency is circulating now, so there is more money." Not one extra dollar was created; people only want to hold more of the existing stock at each interest rate, and the interest rate must rise until they are content holding exactly the quantity that already exists.

    Draw this instead. Money demand (MD) shifts right.

    Exam tip. The payments-institution determinant cuts both ways: anything that lets people transact with smaller balances shifts MD left, and anything that forces bigger balances for the same purchases shifts MD right, while MS moves only when the central bank acts.

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11. 11

    Flight to Liquidity

    The mistake. The specific wrong answer here is shifting MS right because "people are holding more money now." Not one additional dollar was created; the deposits people acquire come from whoever sold them the bonds, so only the willingness to hold money at each rate changed, and the interest rate must rise until people are content holding the fixed quantity that exists.

    Draw this instead. Money demand (MD) shifts right.

    Exam tip. Money demand has an asset motive as well as a transactions motive, so when a stem describes people fleeing bonds for liquidity, shift MD right even though income and the price level never moved.

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12. 12

    Recession and Cash Balances

    The mistake. Students frequently shift MS right here, jumping ahead to the rescue they expect the central bank to mount, or shift MS left because a recession simply feels contractionary. The stem says the central bank takes no action, so the only curve that responds to falling real income is MD, and the interest rate falls as a result rather than as a policy choice.

    Draw this instead. Money demand (MD) shifts left.

    Exam tip. Answer the shock in front of you and not the policy response you anticipate: unless the stem says the central bank acts, a change in real income or the price level shifts MD alone.

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13. 13

    Boom Meets Bond Buying

    The mistake. The dominant wrong answer commits to a direction for the interest rate, almost always by writing "more money in the economy, so the interest rate falls" after reading only the open-market purchase and treating the nominal GDP sentence as background color. The rise in nominal GDP is a genuine money demand determinant that pushes the rate the other way, so the direction of the rate cannot be settled without knowing which shift is bigger. The quantity of money is the one outcome you may state outright, so a student who sounds certain about both is being certain about the wrong one.

    Draw this instead. Money demand (MD) shifts right and Money supply (MS) shifts right.

    Exam tip. When a money-market stem contains two separate shocks, draw both arrows before you read any outcome, and write the sentence "the change in the nominal interest rate is indeterminate, since it depends on the relative magnitudes of the shifts" rather than guessing a direction, because readers award the point for naming the indeterminacy.

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14. 14

    Deflation and Cautious Banks

    The mistake. Students overwhelmingly commit to a direction for the interest rate, writing "deflation and a credit crunch, so the interest rate definitely rises" because the contraction feels like tight money. That answer silently ignores the leftward MD shift, which by itself would lower the rate. A second version of the same error is to declare the rate definitely falls after noticing only the deflation, which ignores MS. Neither reading can be defended without a claim about magnitudes that the stem never makes, and the quantity of money is the only outcome whose direction you can state.

    Draw this instead. Money demand (MD) shifts left and Money supply (MS) shifts left.

    Exam tip. Assign every sentence of a two-shock stem to a determinant before you draw: a price level change belongs to money demand and a change in bank lending behavior belongs to the money supply, and once the two arrows point the same way you must label the interest rate indeterminate instead of picking the direction that feels contractionary.

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15. 15

    Payment Outage, Tighter Rules

    The mistake. The specific error here is importing the supply and demand habit and writing "opposite shifts, so the quantity of money is indeterminate." That reasoning needs an upward-sloping supply curve, and the money supply in the liquidity preference model is vertical, so the quantity is whatever the banking system and the central bank produce and it falls with no ambiguity. The mirror-image error is to move only MS because the reserve requirement is the familiar policy lever and to treat the payment outage as stage dressing rather than as a money demand determinant.

    Draw this instead. Money demand (MD) shifts right and Money supply (MS) shifts left.

    Exam tip. Before calling any money-market outcome indeterminate, check the shape of MS: it is vertical, so the quantity of money is never ambiguous, and the only outcome a combined shift can leave open is the interest rate, and then only when the two curves move in the same direction.

    Try this one on a live graph