Lesson preview · Other Elasticities
Income Elasticity — Normal, Inferior, Luxury
~8 min · Free to read
Get a raise. Do you buy more ramen or ditch it for sushi? Lose your job. Do you cancel Netflix or splurge on designer clothes? Consumers change their habits when their income changes — and that pattern is measured by Income Elasticity of Demand (YED).
Key Term
Income Elasticity of Demand (YED)
Measures how consumers’ purchases of a good respond to changes in income. (‘Y’ is the standard symbol for income.)
Income elasticity — quantity response over percent change in income.
The big difference from PED: the sign matters. YED can be positive or negative, and the sign tells you what kind of good it is. With PED we usually take absolute values; with YED we never do.
Key Term
The Three Categories
Normal good: . Income up → buy more. Most goods. • Necessity (normal): . Demand grows, but slower than income (food, basic clothing). • Luxury (normal): . Demand grows FASTER than income (vacations, fine dining). Inferior good: . Income up → buy LESS (ramen, used cars, store-brand cereal, bus tickets).
Normal goods make up most of what we buy. Earn more, consume more — the question is just how much. Necessities respond modestly (you can only eat so much). Luxuries respond aggressively — get a raise and your vacation goes from Motel 6 to a boutique hotel.
Inferior goods are the strange ones. As people get richer, they buy LESS because they trade up. Ramen noodles, used cars, store-brand cereal, bus tickets. Negative YED isn’t a weird edge case — it’s a whole category of real goods.
Trap · Common Misconception
'Inferior' doesn't mean low quality
An inferior good isn’t bad or defective — the word is technical. It just means consumers buy less of it as their income rises. Store-brand pasta is perfectly edible; people switch to fancier brands when they can afford to. The pasta didn’t get worse; the consumer got richer.
Check yourself · no marks
During an economic boom when people earn more, should ramen noodle producers expect sales to rise or fall?
Commit to one first. Guessing and being wrong beats reading the answer cold.
Worked Example
A household’s income rises from 50,000 dollars to 60,000 dollars per year. Their weekly restaurant spending rises from 100 dollars to 150 dollars. Calculate YED and classify the good.
Practice · 1 / 5
Income rises 5%, quantity demanded rises 10%. What is YED?
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