Verifying a user, such as, but not limited to, a user who answered questions for an unproctered test for employment. A representation of a transition pattern is stored (200). Time series voice data is received from a user responding to a sequence of questions (72) having multiple levels of difficulty. The transition pattern in the voice data (200) is based on a plurality of comparisons (503) of subsets (500) of the voice data corresponding to responses to questions having one or more different levels of difficulty. A further transition pattern (200) is determined from voice data in the same way but based on a shorter sequence of questions (78). The user is verified based on a comparison (78) of this further transition pattern to a previously stored transition pattern.