A biosensor system determines analyte concentration from an output signal generated from a light-identifiable species or a redox reaction of the analyte. The biosensor system adjusts a correlation for determining analyte concentrations from output signals with one or more index functions extracted from the output signals. The index functions determine at least one slope deviation value, .DELTA.S, or normalized slope deviation from one or more error parameters. The slope-adjusted correlation between analyte concentrations and output signals may be used to determine analyte concentrations having improved accuracy and/or precision from output signals including components attributable to bias.