Four Parameter Logistic (4PL) Curve Calculator Documentation

Four Parameters Logistic Curve

Four parameters logistic model (4PL) is often used in modelling of many biological systems. As the result of fitting, an S-shaped curve is obtained. The formula used for fitting is the following:

$$y = \frac{a - d}{1 + (\frac{x}{c})^b} + d$$

where:

a - the minimum value that can be obtained (y at x = 0)

b - Hill’s slope of the curve

c - the point of inflection (i.e., the point on the curve halfway between a and d)

d - the maximum value that can be obtained (y at x tending to infinity)

Data Input

Type the data into the table on the left side of the application. The first column is for x, which is an independent variable, and the second column is for y, which is a dependent variable. You can add rows if you want to introduce more data. You can also paste a dataset from an Excel worksheet using the shortcuts LCTRL+C (Copy) and LCTRL+V (Paste).

Calculation

The best-fit line is calculated automatically. The results are shown below the data table.

Visualize a graph

The fitted curve is visualized automatically. You can export the chart to a png file. Set the graph title and axis labels according to your needs.

A tutorial how to use the Curve Fitting Tool: https://youtu.be/dd2gJ-KSkTU