1. A method, comprising: delivering autonomic neural stimulation (ANS) therapy over a plurality of burst periods, including delivering a burst of stimulation pulses within a portion of each burst period to evoke physiological responses and not delivering stimulation pulses within another portion of each burst period; using a sensor to sense a physiological parameter at a location during the plurality of bursts and recording physiological parameter values for the physiological parameter sensed by the sensor at the location, wherein the recorded physiological parameter values include values corresponding to multiple burst periods, wherein the values corresponding to multiple burst periods include first population data and second population data, and wherein the second population data includes data that is not within the first population data, the first population data including evoked response (ER) values corresponding to the evoked physiological responses to the burst of stimulation pulses for the multiple burst periods, and the second population data including reference values that include no effect (NE) values corresponding to times without an evoked physiological response; quantifying a relationship to identify a difference between the first population data and the second population data; and analyzing the quantified relationship for a signature in the difference between the first population data and the second population data, and comparing the signature to an efficacy signature for a therapy to indicate if the stimulation pulses are evoking desired physiological responses for the therapy, wherein quantifying the relationship between the first population data and the second population data includes: Z-scoring groups of recorded physiological parameter values, including groups of the first and second population data, to obtain Z-scores for each of the groups of recorded physiological parameter values; or T-scoring groups of recorded physiological parameter values, including groups of the first and second population data, to obtain T-scores for each of the groups of recorded physiological parameter values.