4 parameter logistic curve graphpad prism

Top and Bottom are plateaus in the units of the Y axis.The data for this example were taken from a heart failure analysis, and the primary results of this analysis can be seen in the form of the parameter estimates (or more commonly as the hazard ratios). Prism reports both the EC50 and its logartithm Depending on which units Y is expressed in, and the values of Bottom and Top, the EC50 may give a response nowhere near '50'. This is not the same as the response at Y=50. ModelĮC50 is the concentration of agonist that gives a response half way between Bottom and Top. Since the uncertainty of the EC50 is very asymmetric, be sure to choose to compute the confidence intervals using the likelihood ratio asymmetric method.ĭouble click on the X axis of the graph, and choose (at the upper left of the Format Graph dialog) to stretch the axis to a logarithmic scale. If you have subtracted off any basal response, consider constraining Bottom to a constant value of 0. for different treatments, if needed.įrom the data table, click Analyze, choose nonlinear regression, choose the panel of equations 'Dose-response curves - Stimulation' and then choose the equation vs.

Enter one data set into column A, and use columns B, C. Enter response into Y in any convenient units. Enter the concentration of the agonist into X. If you also fit the Hill slope, then it is a four parameter equation. This equation is sometimes called a three parameter dose-response curve. If you have lots of data points, pick the variable slope model to determine the Hill slope from the data. If you don't have many data points, consider using the standard slope model. This is the slope expected when a ligand binds to a receptor following the law of mass action, and is the slope expected of a dose-response curve when the second messenger created by receptor stimulation binds to its receptor by the law of mass action. This model assumes that the dose response curve has a standard slope, equal to a Hill slope (or slope factor) of 1.0. The goal is to determine the EC50 of the agonist - the concentration that provokes a response half way between the basal (Bottom) response and the maximal (Top) response. response curves follow the familiar symmetrical sigmoidal shape. Use a related equation when X values are logarithms of concentrations or doses. This equation is used when X values are concentrations.

4 parameter logistic curve graphpad prism