50 ChroMate
®
Microplate Reader Operator’s Manual Rev. Q
4.4.10 4-Parameter and 5-Parameter Logistic
MODE DESCRIPTION
The 4-Parameter Logistic and 5-Parameter
Logistic non-linear regression models are
commonly used for curve-fitting analysis in
bioassays or immunoassays such as ELISAs
or dose-response curves.
Figure 4.4.10-1 4-Parameter Logistic Model
The 4PL model equation is comprised of 4 parameters:
A = Asymptote at zero concentration: in an ELISA assay where you have a standard
curve, this can be thought of as the response value at 0 standard concentration.
B = Hill Slope or slope factor/steepness of curve: it could be either positive or negative.
As the absolute value of the Hill Slope increases, so does the steepness of the curve.
C = Inflection point: defined as the point on the curve where the curvature changes
direction or signs (concave upwards to concave downwards).
D = Asymptote at infinite concentration: in an ELISA assay where you have a standard
curve, this can be thought of as the response value for infinite standard
concentration.
B = slope factor/steepness of curve
A = asymptote at zero concentration
D = asymptote at infinite
concentration
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