There are several research papers that compare these and other confidence intervals for the binomial proportion. Both Agresti and Coull (1998) and Ross (2003) point out that exact methods such as the Clopper–Pearson interval may not work as well as certain approximations. The Normal approximation interval and its presentation in textbooks has been heavily criticised, with many statisticians advocating that it be not used. The principal problems are "overshoot" (bounds exceed 1), "zero-width intervals" at formula_1 = 0 and 1 (falsely implying certainty), and overall inconsistency with significance testing.