The FTSE Aim all-share index after 18 years remains in negative territory, while smaller companies quoted elsewhere have risen more than three-fold. Paul Marsh, of the London Business School, explains his research into this conundrum to John Authers<br /><br /><br />For more video content from the Financial Times, visit http://www.FT.com/video<br /><br />Subscribe to the Financial Times on YouTube; http://goo.gl/vUQx5k<br />Twitter https://twitter.com/ftvideo<br />Facebook https://www.facebook.com/financialtimes
