Read this: As of the 2015–16 season, Premier League football has been played in 53 stadiums since the formation of the Premier League in 1992. The Hillsborough disaster in 1989 and the subsequent Taylor Report saw a recommendation that standing terraces should be abolished; as a result all stadiums in the Premier League are all-seater. Since the formation of the Premier League, football grounds in England have seen constant improvements to capacity and facilities, with some clubs moving to new-build stadiums. Nine stadiums that have seen Premier League football have now been demolished. The stadiums for the 2010–11 season show a large disparity in capacity: Old Trafford, the home of Manchester United has a capacity of 75,957 with Bloomfield Road, the home of Blackpool, having a capacity of 16,220. The combined total capacity of the Premier League in the 2010–11 season is 770,477 with an average capacity of 38,523.

Since which leagues creation have football grounds in Old Trafford seen steady improvements?
What is the answer? (If it cannot be answered, return "unanswerable")
unanswerable