In a statement released today, Marcel Rohner, UBS's new chief executive, conceded that the bank relied too heavily on historical data to measure its risks. “The structural underlying problem is the way we focused a lot on very illiquid, long-dated risk, and at the same time let our balance sheet grow rather rapidly and provided our funding resource almost freely. We kind of drove the business growth into this high-volume, high-liquid, high-grade exposure,” he said."What has happened is that what was historically very safe and low volatility turned, through the very serious market dislocation in the US mortgage-backed securities market, into a high-correlated credit type of exposure. This was not foreseen by our risk framework,” continued Rohner.The bank still holds $19 billion in residential mortgage-backed securities, and $4 billion at the current levels, whose index equivalent is about $5.5 billion. Rohner believes the bank can hedge this exposure, and so is comfortable with owning it.As was expected, management changes were also announced. Huw Jenkins, chief executive and chairman of the investment banking division, will be replaced by Rohner. Jenkins will continue in a senior advisory role. Marco Suter, currently executive vice-chairman, will take over Clive Standish’s role as the bank’s chief financial officer. Standish plans on retiring. Joseph Scoby will replace Walter Stuerzinger as chief risk officer, with Stuerzinger becoming chief operating officer.