Generally, the stock price indices are classified into two different categories namely global indices and national indices, the national indices, which are more commonly quoted, represent the performance of the stock market of given country such as Brazil's BOVESPA, India's NSE or BSE, China's Hang Seng or the Shanghai SE Composite Index...etc, these type of indices are provided by the local financial authorities. The global equity indices, on the other hand, are calculated and provided by world agencies such as Thomson DataStream, Standard and Poor, Morgan Stanley...etc. In addition, these agencies also offer stock price indices at country level, the methodology used to calculate the stock price index may differ from agency to another, which may affect the return and volatility. For instance, the datastream market indices offer stock prices indices for 53 countries all over the world, each index covers at least 75-80% of market cap of the publicly listed companies in the country. The Standard and Poor agency has its own indices known as the Broad Market Index (BMI) and covers most of the developed and emerging countries, the method used by Standard and Poor to calculate the stock price index is called the adjusted float or free float methodology, which according to "Investopedia" is the best measurement of stock price movements. The same methodology is used by other agencies such as Morgan Stanley (MSCI), Financial Times and Stock Exchange (FTSE). The investors frequently use these indices as benchmarks for their equity portfolios.

As previously mentioned, these global agencies maintain a record of stock price index for many countries, even sometimes for period longer than the periods covered by national indices.

So, are these global indices suitable for academic researches and papers? Is it used in academic researches, especially in researches concerned with stock prices volatility? or it can only be used as benchmarks?