Wall Street's Dow Jones Industrial Average - one of the world's best known measures of stock market performance - is to be revamped.

Aluminium producer Alcoa, Bank of America and Hewlett-Packard are being dropped from the index of the top 30 US companies.

The companies have low share prices, so have little influence on the index.

From 23 September they will be replaced by investment bank Goldman Sachs, Nike and Visa.

The make-up of the Dow has only been changed 49 times in its 117 year history.