One problem with the consumer price index stems from the fact that, over time, consumers tend to buy larger quantities of goods that have become relatively less expensive and smaller quantities of goods that have become relatively more expensive. This problem is called .

SUBSTITUTION BIAS

Explanation:

Substitution bias occurs when a customer decides to purchase a substitute of a good after the prices becomes cheaper than the goods they normally purchase. It rises as a problem in price index due to the fact that customers/buyers can decide to change or substitute goods at an instant because of changes in prices. In situations like this, customers tend to avoid the whole increase in prices by changing to cheaper substitutes. Substitution generally is a consumer changing or substituting an expensive product for a cheaper one due to changes in prices. This usually leads to inflation rate been overestimated or overstated.

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