A collectible market index is a tool used by collectors and investors to track values of collectibles against collectors market from a specific date, calculated in form of Index. It measures the value of a section of the collectors market.

Collectible market indices have been criticised for often being a poor guide to investors. They are sometimes too broad; a sub-category of a collectible may actually be going down in value while the index shows the category going up. This criticism has been levelled against the indices produced by Sotheby's auction house. An index may be based on a fixed "shopping basket" of individual items. This can be an unrealistic indicator of true market trends when collectors' preferences change, or if only the top end of the market is represented. This kind of approach was adopted in the multiple indices produced by Salomon Brothers, and the Market Bradex of The Bradford Exchange. Market indices do not usually include costs. These include auction fees, storage, and insurance. Such costs can be substantial. They can make a significant difference to whether an investment is worthwile even if the market index shows a rising trend.

A collectible market index can be constructed by combining the indices of a number of individual items. The volatility of the individual prices is assumed to follow a diffusion process with a log-normal distribution. The index is extracted by a least squares analysis. The individual item indices are then combined as a weighted mean index. This approach was first developed for tracking property prices in 1991.

List of indices

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