The difference between change in quantity demanded and change in demand lies in what causes the movement and how it is represented on the demand curve:

• Change in Quantity Demanded refers to a movement along a fixed demand curve caused only by a change in the price of the good or service. When the price decreases, quantity demanded increases (movement down the curve), and when the price increases, quantity demanded decreases (movement up the curve). This does not shift the demand curve itself but moves the point along the curve

• Change in Demand refers to a shift of the entire demand curve either to the right (increase in demand) or to the left (decrease in demand). This shift is caused by factors other than the price of the good, such as changes in consumer income, preferences, prices of related goods (substitutes or complements), expectations, or other external factors. A change in demand means that at every price, the quantity demanded changes, reflecting a new demand relationship

Summary in Table Form

Aspect| Change in Quantity Demanded| Change in Demand
---|---|---
Cause| Change in price of the good| Change in non-price factors (income, tastes, etc.)
Movement on Demand Curve| Movement along the same demand curve| Shift of the entire demand curve (left or right)
Effect on Quantity| Quantity demanded changes at a specific price| Quantity demanded changes at all prices
Example| Price of soda drops, so more soda is bought| Increase in income leads to more soda demanded at all prices

In essence, a change in quantity demanded is a price-driven movement along the demand curve, while a change in demand is a shift of the demand curve caused by other factors affecting consumer behavior