Which of these effects does not represent a change in demand?

The correct answer reflects the concept that changes in price lead to movements along the demand curve rather than shifts in the demand curve itself. In economics, a change in demand refers to a shift of the entire demand curve, which results from factors other than the good's price, such as consumer preferences, income levels, or the prices of related goods.

When the price of a good increases, the quantity demanded decreases, illustrating the law of demand; this results in a movement along the curve rather than a change in the demand itself. Conversely, options that discuss changes in consumer preference, consumer income, or a decrease in price leading to an increase in quantity demanded all represent shifts in the demand curve, as they indicate a change in consumers' willingness or ability to purchase the good at various price points. Thus, option A correctly identifies a scenario that does not depict a change in demand.