Products or services that partly or wholly satisfies the same consumer need or want as another product / service. Examples include tinned meat and fresh meat, and travelling by train instead of travelling by car. These are, however, not perfect substitutes. A closer substitute may be tinned tuna and tinned salmon. But this is still not a perfect substitute. Perfect substitutes only exist where the quality of the product / service is considered to be identical. This may be the case for different brands of cereal, for example. In demand theory, if the price of a substitute product or service decreases then it is likely that demand for the substitute product or service will rise. Hence, an important factor affecting demand is price in relation to that of competitor products.