Explanation:

- Number of consumers in the market: This affects market demand rather than individual demand. An increase or decrease in the number of consumers changes total market demand, not the demand of an individual.

- Distribution of income: While this can affect demand patterns across different groups, it is more related to market demand as a whole rather than individual demand.

- Age of the sample population: This factor influences demand preferences across demographics but doesn't directly impact individual demand unless age affects preferences.

- Income of the consumer: This directly affects individual demand as a higher income generally increases an individual's ability to purchase goods and services.