Change in demand vs change in quantity demanded: what's the difference?

You wrote "demand fell." Did you mean demand, or quantity demanded? In IB Economics they're different claims — and mixing them up costs marks.

You write: "the price went up, so demand fell."

That sentence loses marks. Not a typo, not a phrasing quibble — in IB Economics, "demand" and "quantity demanded" are two different claims, and the examiner reads them as two different things. Say one when you mean the other and your answer describes the wrong event.

Here's the fix, and it's one sentence: a change in the good's own price changes quantity demanded. Only a non-price determinant shifts demand.

The two phrases are not interchangeable

Quantity demanded is a single point — how much people buy at one specific price.

Demand is the whole relationship — how much people buy across every price. The entire curve.

So when the price of a good rises and people buy less of it, demand hasn't changed. The quantity demanded has. People are responding to a higher price along the same curve — the relationship between price and quantity is exactly what it was.

Demand only shifts when something other than the good's own price changes. Then people buy more or less at every price — and that's a new curve.

The sentence the examiner wants

A change in the good's own price changes quantity demanded, not demand.

Write that sentence and you've shown the examiner you hold the distinction. Most students don't — they write "demand fell" for a price rise, and the marker has less to reward, because the claim is wrong as written — even if the diagram is trying to show the right idea.

Where it costs you

It costs marks twice. In the written answer, "demand fell" after a price rise is a wrong statement, so the analysis is weakened from the first step. In the diagram, if you believe demand fell you'll shift the whole curve left — when the correct answer is a movement along it. One wrong word, multiple places to lose credit — and the error compounds through every follow-on point that builds on it.

Mia catches this in real time

Students don't lose marks from not knowing the topic. They lose marks because they've written "demand" for "quantity demanded" so many times it feels right.

When you tell Mia demand fell because the price rose, she stops you on the word — names which event you actually described, and makes you rewrite the sentence before it's muscle memory in the exam.

Stop practising the wrong answer.

Mia spots the misconception, fixes the thinking, and makes you redraw it correctly.

Across the full IB Economics and Business Management curriculum. Free to start. No card needed.