For those who think making sense of financial data presents a challenge, consider this: Aaron Bell’s advertising technology firm wrangles a trove of data that is 150 times bigger than the data on all US stock exchanges combined.

His ad trading start-up, AdRoll, specialises in ad retargeting. It looks at internet users' browsing histories and ensures that as users surf, they keep seeing advertisements for products in which they have shown interest. Based in San Francisco, AdRoll uses its analysis of web data to help advertisers buy online ad space.