Which of these is not a factor affecting demand?

The correct answer identifies changes in government policy as not being a direct factor affecting demand in the same way as the other options. Demand refers specifically to consumers' willingness and ability to purchase goods and services at various price points.

Changes in population can significantly influence demand; for example, an increase in population can lead to higher demand for certain goods and services. Similarly, changes in personal income directly affect consumer purchasing power, influencing how much consumers can afford to buy. Changes in fashion or popularity also play a crucial role, as trends can boost demand for specific products quickly, affecting their market success.

While government policy can impact overall market conditions and influence businesses (such as through regulations, taxes, or subsidies), it does not directly alter the demand for specific products. Instead, government policy affects the environment in which demand exists, making it less of a direct factor in consumer demand compared to the other options listed.