Matrix elements for ionisation play an important part in electron-atom scattering calculations. Two methods for describing ionisation that can be incorporated into a scattering calculation are tested here against coplanar asymmetric experimental differential cross sections at 150 and 250 eV. They are the distorted-wave Born approximation and the coupled pseudostates method. A method that incorporates the exact boundary condition for three charged bodies describes the data significantly better and shows an important direction for improvement of scattering calculations.