UBS has lifted its target price for insurance group Aviva from 380p to 450p and reiterated its buy rating on the stock."We like Aviva's share price, but there is plenty about the business that worries us. However, we think the new chairman will address these concerns once his appointment is confirmed on 3rd May," said analysts James Pearce and Angela Gu.They said that ongoing benefits from the ECB's long-term refinancing operation (LTRO) and further disposals could also provide helpful newsflow, and the valuation "looks compelling".The stock is trading at seven times earnings, 35% lower than the sector average multiple of 10.8.BC