Concept:Index numbers are statistical measures that combine multiple characteristics of the data into a single relative value.
Explanation:An index number compares the level of a variable (like price or quantity) between two time periods, expressing it as a relative change.
It is a special type of average because it summarizes a set of related data points using a weighted or unweighted mean.
It is often expressed as a percentage relative to a base period (e.g., 120 means 20% increase).
All three statements—measure of relative change, special average, and percentage relative—are correct descriptions.
Answer:Index number is a measure of relative change, a special type of an average, and a percentage relative.