4-parameter fit

[Guest]

Just wondering if anyone knows a way to add a 4-parameter fit to a curve in Excel. Any help would be greatly appreciated. Thanks.

 

[Tushar Mehta]

What is a four parameter fit? Is it like the real estate example in XL
help for the LINEST function? Or is it like
http://www.stfx.ca/people/bliengme/ExcelTips/Polynomial.htm ?
--
Regards,

Tushar Mehta
www.tushar-mehta.com
Excel, PowerPoint, and VBA add-ins, tutorials
Custom MS Office productivity solutions

 

[Jerry W. Lewis]

Depends on what 4-parameters you want to fit. The 4 coefficients of a
cubic polynomial can be fit with LINEST. If the equation is not linear
in the unknowns (such as a 4-parameter logistic), then you could use
Solver to find the parameters that minimize the sums of squares.

Jerry

 

[precisely]

4 parameters in typical biological systems of curve fitting are:

(1) TOP (highest value) -- This could be dervied from using an asymptote value
(2) BOTTOM (lowest value) -- This could be dervied from using an asymptote value
(3) SLOPE of the line connecting top and bottom (Often used as Hill Slope)
(4) CONSTANT or EC50 value

Use Graphpad for ease. Academic license and student licenses are, while not affordable in Asian countries,affordable for Western Europe, Canada and US.

Graphpad should do something for allowing more users in Asian countries make software available for day's salary (3 dollars), otherwise Rapidshare is easy way to get access to Graphpad (or other software).

I do support software piracy on economic status mitigation.

 

[miraibio]

4 Parameter Logistic

The 4 Parameter Logistic (4PL) nonlinear regression model is commonly used in bioassay or immunoassay analysis such as ELISA or dose-response.

It's key characteristics are:

• Symmetric - The sigmoidal curve that the 4PL generates is symmetric around the inflection point.
• Monotonic - The function is either always increasing or decreasing.

Here is a blog post I've written that explains the 4 Parameter Logistic model equation in more detail with pictures =)

Allen Liu
MiraiBio

 

[josephrcoouto]

Here is a link to a file that I have on google docs available to everyone. It has 4 parameter curve fitting that's ideal for ELISAs. Fit the curve to the data either manually or by using solver. You can also calculate unknown samples
http://docs.google.com/leaf?id=0B8GKGvXVgyhwZmIwOWZkZGUtZTA1OS00ODBhLTg0ODQtOThlMDRmNTJiMmFl&hl=en

 

[ericvandamme]

Just wondering if anyone knows a way to add a 4-parameter fit to a curve in Excel. Any help would be greatly appreciated. Thanks.

I haver recently come across a 4PL fit in excel at www.ivdtools.com

 

[josephrcoouto]

I have a file that you can download from my linkedin page
http://www.linkedin.com/pub/joe-couto/6/660/347
(or google joseph couto antibody engineering)
Scroll to the bottom and click the yellow button "view full profile" and then scroll again to the bottom of my profile. I got two excel files there and the 4-parameter curve fitting is one of them.