Investors in bank stocks should take the latest round of quarterly earnings with a pinch of salt, given the effects some contentious accounting metrics have had on their income statements, according to market observers.

Debit valuation adjustments, an accounting rule that permits banks to post paper profits when the value of their own credit quality declines, helped Citigroup post a $3.77bn profit yesterday even as its revenue fell. And JP Morgan Chase included a $1.9bn pre-tax benefit from debit valuation adjustments in its investment bank when it posted third quarter earnings last Thursday.