Dose response curve linear equation

[UGLYFROG]

I have done a dose response curve and I have done a linear line to get the equation which I need to work out the value of something else. However, my equation follows the format of y =mx - c but i am confused as i thought it is meant to be y = mx + c? Could someone help with what the issue is here?

[joeu2004]

First, it would help if you were more specific. At the very least, provide the specific Excel formulas, not math abstractions. Even better, attach an Excel file that demonstrates the issues raised in your question. See the bright yellow banner at the top of this webpage for attachment instructions.

Note that y = mx - c can be written y = mx + (-c). In other words, "c" is simply a negative intercept in your form y = mx + c.

Aside.... I would be interested in seeing your dose-response curve, and the formula that generates it, if any. I just participated in a discussion where that came up. I might learn from your example.

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PS.... AFAIK, a dose-response curve is s-shaped. So why are you fitting a linear equation to it? Would you prefer to fit an s-shaped (sigmoid) function to the dose-reponse data?

If so, I will definitely need that Excel file attachment with the data.

[hrlngrv]

Mathematically there's NO DIFFERENCE between y = m x - c and y = m x + c. The only difference would be the sign of the fitted value of c. Since subtracting -3.5 is identical to adding +3.5, this is po-TAY-toes, po-TAH-toes, different way of expressing the same thing.

ADDED: I don't work in biostats/pharmaceuticals, but I expect there may be underlying interpretative meaning between positive and negative constant intercepts, and such interpretations would involve psychological bias and maybe whether test subjects would have preconceptions whether they were given placebos.

[UGLYFROG]

Thanks for your reply, I have attached an image of the curves and equations. Attachment 714782

I am trying to fit a linear equation in order to work out the IC50 value.

[UGLYFROG]

Sorry just realised I didn't tag you, not sure how this works

[UGLYFROG]

Mathematically there's NO DIFFERENCE between y = m x - c and y = m x + c. The only difference would be the sign of the fitted value of c. Since subtracting -3.5 is identical to adding +3.5, this is po-TAY-toes, po-TAH-toes, different way of expressing the same thing.

ADDED: I don't work in biostats/pharmaceuticals, but I expect there may be underlying interpretative meaning between positive and negative constant intercepts, and such interpretations would involve psychological bias and maybe whether test subjects would have preconceptions whether they were given placebos.

Thanks for your reply!

[UGLYFROG]

First, it would help if you were more specific. At the very least, provide the specific Excel formulas, not math abstractions. Even better, attach an Excel file that demonstrates the issues raised in your question. See the bright yellow banner at the top of this webpage for attachment instructions.

Note that y = mx - c can be written y = mx + (-c). In other words, "c" is simply a negative intercept in your form y = mx + c.

Aside.... I would be interested in seeing your dose-response curve, and the formula that generates it, if any. I just participated in a discussion where that came up. I might learn from your example.

-----

PS.... AFAIK, a dose-response curve is s-shaped. So why are you fitting a linear equation to it? Would you prefer to fit an s-shaped (sigmoid) function to the dose-reponse data?

If so, I will definitely need that Excel file attachment with the data.

Thanks for your reply, I have attached an image of the curves and equations. Attachment 714782

I am trying to fit a linear equation in order to work out the IC50 value.

[joeu2004]

Cannot access Attachment 714782. Be sure that it is an Excel file, not an image file. When I say "Excel file", I mean: saved as xlsx, xlsm or xls.

[Glenn Kennedy]

Hi there.

A picture is worth 1,000 words. An Excel sheet is worth 1,000 pictures.

Please re-read the yellow banner about sample worksheets, at the top of the screen. Act on its guidelines and post a SMALL sample sheet.