Her Majesty's Revenue and Customs routinely measures and monitors various performance matrix, including yield-to-cost ratios and a number of statistical models. These were used as part of the spending review process to estimate the effect of investing resource to support its compliance strategy. On the basis of this analysis, HMRC estimates that the additional expenditure of £900 million over the spending review period will result in an extra £7 billion of yield per year by 2014-15.