Investment company Alliance Trust increased net asset value by 6.8% in the half-year and achieved total shareholder return of 8.8%.Net asset value rose to 338.3p as at 31 July from 316.8p as at 31 January. Total shareholder return for the six-months period compared to a total return of 14.2% on the FTSE All-World Index.The group paid an interim dividend of 2.025p per share and said it would pay a final dividend of at least 2.025p in April 2010.'Looking forward, we expect the recovery of the global economy to be a long process, but we strongly believe that with our long term conviction-based investment approach, Alliance Trust is well-positioned to continue to deliver superior returns to investors,' said chief executive Katherine Garrett-Cox.However, the group added that it does not expect the recovery to be 'smooth or rapid.'