In Datastream you can find the current beta (a measure of the volatility of a share) with datatype Mnemonic BETA in a static request. Worldscope and Thomson Financial also offer their current beta (available with the Excel add-in). The method of calculation is different in these three databases, so check the definition and calculation method!
Historical beta’s are more difficult to get. Datastream offers a historical beta (Mnemonic = 897E) , but you have to check their calculation method to see if you agree with this method. Datastream uess a five year period, and the share price is regressed “against the respective Datastream total market index using log changes of the closing price on the first day of each month”. Which Datastream total market index is used, can be retrieved from Datastream, by requesting in a static request the datatype Assoc Market Index – Datastream (Mnemonic = INDX) of the equity.
More information about the calculation of the historical beta by Datastream can be found in Extranet: http://extranet.datastream.com/Codes/Economics/69Chan/69Beta.htm When you have to login, please use the creditials used for Datastream Navigator.