https://elisaanalysis.com/

Hello Ayesha,

You need to transform your x axis variables to logarithmic scale before doing 4LP in GraphPad. I have used this to determine (so-called) IC50 values in viability assays. It is under the Dose-response analysis menu of XY graphs.

Here is the help page of Prism:

https://www.graphpad.com/guides/prism/7/curve-fitting/index.htm?reg_dr_inhibit_variable.htm

Why one needs 4LP? It is beyond my maths skills to explain, but the article below was the reason for me to use this fitting method.

Article Guidelines for accurate EC50/IC50 estimation

Hope this helps, good luck.

Hi Ayesha,

I completely agree with Caner. You need to log transform your X-axis variables; X is log (concentration) and use non-linear regression analysis in GraphPad prism. I am also attaching the snapshot of GraphPad prism page, where you can select the right option.

All the best!

Hiba Riyadh Al-abodi , Rajesh Kumar , Caner Geyik Thank you all for your help! I had no idea I had to log transform the X-axis variables and so once I did that, I was able to graph it on GraphPad. The wonderful and helpful ResearchGate community never fails to amaze me! :-)

I had no idea what 4-parameter test is. I sent an e-mail to the company which produces the kit I used. They sent me back an excel file with macros to calculate my results. Why don't you do the same?

not sure if you have done this by now. But there is a free online program called My Assay that does this all for you.

I have done that, but it is not accurate. Try put the OD of the known standard and but the same OD for X and see that.