Prism offers built-in equations designed to handle X values as either concentration OR log(concentration). Note that the X values are logarithms of concentration.From the Welcome dialog, choose the XY tab, drop the list of sample data sets and choose "RIA or ELISA".Top and Bottom are plateaus in the units of the Y axis.Prism can easily fit a dose response curve to determine the IC 50. Depending on which units Y is expressed in, and the values of Bottom and Top, the IC50 may give a response nowhere near "50". This is not the same as the response at Y=50. IC50 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 - Inhibition" 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 concentrations of the inhibitor into X. 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 curves has a standard slope, equal to a Hill slope (or slope factor) of -1.0. The goal is to determine the IC50 of the inhibitor - the concentration that provokes a response half way between the maximal (Top) response and the maximally inhibited (Bottom) 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 or doses.
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