Many other factors besides price can affect the demand for goods. For example, if it was discovered that tomato sauce was extremely good for your health, demand for pizza would rise. Consumers would want to buy more pizza at all price levels. This increase in demand shifts the entire demand curve to the right. If it was announced that tomato sauce was unhealthy, then people would buy less pizza at all price levels. This decrease in demand shifts the demand curve to the left.

     Other factors can shift the demand curve. For example, if your income were to rise, you might buy more pizza. Higher income causes people to buy more of most goods at every price level. This creates a shift to the right of the demand curve. Similarly, a decrease in income causes demand for most goods to fall.

     Changes in population will affect demand. For example, an increase in the number of senior citizens is likely to increase the demand for medical care. Advertising and fashion trends can also have a big effect on consumer demand.

     The demand for one good can also affect the demand for other goods. Complements are two goods that are bought and used together. People who buy skis are likely to buy ski boots. Substitutes are goods used in place of one another. When people buy more snowboards they will buy fewer skis.