The distorted-wave Born approximation (DWBA) has special theoretical significance because it is possible to calculate scattering to low-lying states of an atom using an optical potential to describe higher target states, including the continuum, for which DWBA is the only approximation. The double differential cross section gives a representation of integrated cross section data that is convenient for assessing the validity of the DWBA in the optical potential context. For primary and secondary electrons from helium at 100, 300 and 500 eV the DWBA represents larger cross sections very well. For smaller cross sections it is an overestimate.