STAMP MARKET INDEX

Just read that there is a Stamp Market Index for US Stamps. I think it is composed of a basket/selection of stamps (ie 1930s Zeppelin, 1893 Colombian commemoratives, the first airmails etc)whose prices are tracked and used as basis to see trends in the market prices of US stamps. It was mentioned though that the index does not include stamps before 1890 and the modern commemoratives of the 1980s and 1990s.

It is very interesting to know that sort of a DJIA (Dow Jones Industrial Average - stock index for US equities/stockmarket)or PSEi(Philippine Stock Exchange Index of the Philippine Stockmarket) type of index has been developed/used for stamps. No wonder some consider stamps as investments.

Back to the US stamp index; is there only one such index? Or are there several? Are there different classifications of indices; such as by date? What stamps are included in the index? What determines inclusion in the index? What trends are seen recently? When did indexing start? Can this be used to predict future prices just like equities analysts use technical analysis and charts? Do other countries have this stamp index?
Stamp collecting sure is serious business!