Which factor is a common cause of increased demand for a product?

Increased consumer income is a common cause of increased demand for a product because as individuals' incomes rise, they typically have more disposable income to spend on goods and services. This increased purchasing power allows consumers to buy more of the products they desire, thus increasing demand. For many products, especially those considered normal goods—items for which demand increases as income increases—this relationship is quite pronounced.

Higher consumer income can lead to a greater willingness and ability to purchase, driving demand up for a variety of items. This is particularly relevant in markets where consumers are more likely to spend on higher-quality or luxury goods as their financial situation improves. Consequently, businesses may respond to this increased demand by increasing production or adjusting prices, further influencing market dynamics.

In contrast, factors such as decreased population growth or consumer disinterest would lead to a decrease in demand, while higher prices of substitutes typically encourage consumers to switch to alternatives, which does not contribute positively to the demand for the original product in question.