 While benchmarks may have much greater uniformity of instrument type than managed portfolios, the sheer number of securities – and the data maintenance issues required to reprice each one, and to ensure that the correct coupon amount and timing is used when a coupon is paid – means that detailed benchmark modeling remains extremely difficult.There are also issues involving transparency of benchmark calculations, with many of the underlying actions remaining obscure.Even pricing data can be difficult to come by in some cases.