Welcome to Inflation & Deflation!

Hey everyone! Ever wonder why the price of your favourite bubble tea or lunch box seems to go up over time? Or why your parents talk about how much cheaper things were "back in their day"? The answers lie in the concepts of inflation and deflation.

This is a super important topic because it affects everyone's money – from your personal savings to the entire Hong Kong economy. Don't worry, we'll break it down into simple, easy-to-understand parts. Let's get started!


1. Defining Our Key Terms

First things first, let's get our main definitions straight.

What is Inflation?

In simple terms, inflation is when prices for most goods and services are rising. The formal definition is:

Inflation is a sustained increase in the general price level.

Let's break that down:

  • Sustained increase: This isn't a one-time price jump. The prices have to keep rising over a period of time (e.g., month after month).
  • General price level: This means it's not just one or two items getting more expensive. It's a broad increase in the average price of many goods and services across the economy, like food, transport, housing, and entertainment.

Analogy: Think of your money's buying power like a phone battery. Inflation slowly drains that battery. The same \$50 buys you a little less today than it did last year.

What is Deflation?

Deflation is the exact opposite.

Deflation is a sustained decrease in the general price level.

This is when the average price of goods and services is continuously falling. While falling prices might sound great, it can actually be a big problem for the economy, but we'll get into the effects later!


Quick Review: Key Definitions

Inflation = Sustained RISE in general price level.
Deflation = Sustained FALL in general price level.

Common Mistake to Avoid!

A common mistake is thinking that if the price of iPhones goes up, it's inflation. Not necessarily! Inflation is about the average price of a whole basket of goods and services rising, not just a single product.


Key Takeaway for Section 1

Inflation and deflation describe the direction of the economy's average price level over time. Inflation means your money buys less, while deflation means it buys more.


2. Nominal vs. Real Interest Rates: What's the Difference?

When we talk about inflation, the interest rates you see at the bank don't tell the whole story. We need to distinguish between what's written on paper (nominal) and what it means for your actual purchasing power (real).

What are Nominal and Real Interest Rates?
  • Nominal Interest Rate (\(r_n\)): This is the interest rate as advertised by a bank. It's the rate of growth of your money in dollar terms. If you put \$100 in an account with a 5% nominal interest rate, you'll have \$105 in one year. Simple!
  • Real Interest Rate (\(r\)): This is the interest rate after accounting for inflation. It tells you the rate of growth of your purchasing power. It answers the question: "How much more stuff can I actually buy?"
The All-Important Formulas

The relationship before the event is based on the expected inflation rate:

\(\text{Nominal Interest Rate} = \text{Expected Real Interest Rate} + \text{Expected Inflation Rate}\)

Often, it is rearranged to find the expected real interest rate:

\(\text{Expected Real Interest Rate} = \text{Nominal Interest Rate} - \text{Expected Inflation Rate}\)

After inflation actually happens, we calculate the realised (actual) real interest rate:

\(\text{Realised Real Interest Rate} = \text{Nominal Interest Rate} - \text{Actual Inflation Rate}\)

Let's see it in action:

Example: You deposit money in a bank that offers a 4% annual nominal interest rate. You expect the inflation rate to be 3%.

Your expected real interest rate is: \(4\% - 3\% = 1\%\).

If the actual inflation rate turns out to be 6%, your realised real interest rate is: \(4\% - 6\% = -2\%\). Your purchasing power actually drops!


Key Takeaway for Section 2

The nominal interest rate is the sticker price, but the real interest rate is what really matters for your wealth because it accounts for the effects of inflation on your purchasing power.


3. The Redistributive Effects of Unanticipated Inflation

What happens when inflation is a surprise? When actual inflation differs from expected inflation (\(\text{Actual Inflation Rate} \neq \text{Expected Inflation Rate}\)), it creates unexpected winners and losers. This is called a redistributive effect – it shifts wealth between groups.

a) Debtors (Borrowers) vs. Creditors (Lenders)

When actual inflation is higher than expected, the realised real interest rate is lower than the expected real interest rate.

  • Debtors (Borrowers) GAIN from unanticipated inflation. Why? They borrow money when it has high purchasing power but repay the loan later with money that has lower purchasing power than expected. In real terms, their debt becomes cheaper to pay off.

  • Creditors (Lenders) LOSE from unanticipated inflation. Why? They receive loan repayments whose purchasing power is lower than anticipated, meaning their realised real return is lower.

Simple Example: David (debtor) borrows \$1,000 from Carol (creditor) at a fixed nominal rate. If unanticipated inflation occurs, the money David repays buys fewer goods and services than expected. David gains, and Carol loses purchasing power.

The opposite is true for unanticipated deflation: Debtors lose because they repay with money that is worth more, and creditors gain.

b) Holders of Monetary Assets vs. Real Assets

Unanticipated inflation also affects people based on what kinds of assets they own.

  • Monetary Assets are assets with a fixed money value, like cash or money in a savings account. Holders of these assets LOSE during inflation because the purchasing power of their fixed amount of money falls. Your \$100 bill will still be a \$100 bill, but it will buy fewer things.

  • Real Assets are physical assets like property, gold, or artwork. Holders of these assets are often protected or may even GAIN during inflation. This is because the nominal price of these physical items tends to rise along with inflation, preserving their real value.

Did you know?

This is why people often see property as a 'hedge against inflation'. They believe the value of their apartment will increase over time, protecting their wealth from being eroded by a general rise in prices.


Key Takeaway for Section 3

Unanticipated inflation isn't fair to everyone. It redistributes wealth from creditors (lenders) and holders of monetary assets TO debtors (borrowers) and holders of real assets.


4. A Simple Theory of Inflation: The Quantity Theory of Money

So, what causes inflation? One of the oldest and simplest explanations is the Quantity Theory of Money. It connects the amount of money in an economy directly to the price level.

The Equation of Exchange

The theory starts with a famous equation called the Equation of Exchange:

\(MV = PY\)

Let's break down each letter:

  • \(M\) = Money Supply: The total amount of money circulating in the economy.
  • \(V\) = Velocity of Circulation: The average number of times a unit of money is spent on final goods and services in a year. Think of it as how fast money is changing hands.
  • \(P\) = General Price Level: An average of the current prices.
  • \(Y\) = Real Output (Real GDP): The total quantity of goods and services produced in the economy.

The equation \(MV = PY\) is an identity that states total nominal expenditure (\(MV\)) equals total nominal output (\(PY\)).

From an Equation to a Theory

To turn this into a theory that explains inflation, we need to make some assumptions.

Assumption 1: Both \(V\) and \(Y\) are constant.

The classical theory assumes that \(V\) (people's spending habits) and \(Y\) (full employment output) are stable in the long run. If \(V\) and \(Y\) are fixed, any change in \(M\) leads to a strictly proportional change in \(P\).

Conclusion: Under these assumptions, the price level is directly proportional to the money supply. If the money supply (\(M\)) increases by 8%, the inflation rate will also be 8%.


Assumption 2: Only \(V\) is constant.

This assumption allows real output (\(Y\)) to grow. Expressed in percentage change form:

\(\%\Delta P = \%\Delta M - \%\Delta Y\)

(Where \(\%\Delta P\) is the inflation rate)

This shows that the inflation rate is the growth rate of the money supply MINUS the growth rate of real output.

Conclusion: Inflation occurs when the money supply grows faster than real output. It's the classic idea of "too much money chasing too few goods".

Example: If the money supply (\(M\)) grows by 10% in a year, and real output (\(Y\)) grows by 4%, the inflation rate will be: \(10\% - 4\% = 6\%\).


Key Takeaway for Section 4

The Quantity Theory of Money proposes a direct link between the money supply and the price level. When money supply growth exceeds real output growth, inflation results.