Conversely if the YED of a product is negative then we would expect it to be an inferior good and so an increase in income would result in a decrease in the QD of the inferior good (a decrease in income would result in an increase in QD).

If prices were to change on a product (i.e. increase) then consumers’ real income would fall (assuming wages don’t increase). This is because their income is the same, but the amount they can by with it has been reduced due to the increase in the price of a good (one’s real income would only really fall if a lot of goods were to increase in price, particularly on goods such as petrol and food).