Clarification on the Income and Cross Elasticity concept

GoodBoil SG

Some text/ notes say PED is the % change in DD for a good due to a change in the income of the consumers while some say it is the % change in QUANTITY Demanded.. I know for a fact that in calculation we use QDD but when explaining, do we stick to using change in DD instead of change in QDD? I remember my teacher once explained it ages ago.. Cant find any notes that I jot down.. So which is which..? And the proper way to explain? Thanks! O.o

SBS2601D SG

You just answered your own question.

Use in words, what you use in calculations.

DD and QDD are 2 completely different concepts.

The former refers to the demand schedule for EVERY combination of price-output, the latter is for the quantity demanded at A GIVEN price.