11. A computer-readable storage device having instructions stored for controlling a computing device to perform operations comprising: receiving a plurality of stored speech samples of a same word for verifying a user; comparing each of the plurality of stored speech samples to each other, to yield a variance over time; receiving speech from the user, distinct from the plurality of stored speech samples, to be verified; receiving a parameter that identifies a certainty level associated with the variance, from a plurality of certainty levels, to be applied when verifying the speech as authentic; based on the certainty level, verifying the speech as authentic, to yield a verification; and transmitting access data based on the verification.
15. The computer-readable storage device of claim 11 , wherein each certainty level of the plurality of certainty levels is associated with a different user.