four-parameter logistic equation
Author Message
four-parameter logistic equation

Hi

I am having problems trying to get Excel to do a four-parameter
logistic equation using the solver add-in.

y=Bottom + ((Top - Bottom) / (1+ 10(logEC50-X).HillSlope))

Can anyone tell me if I am asking too much of Excel.

I have some values got from a curve fitting program (Prism) but when I
pull them into my equation the curve is no where near the orginal raw
data.

Any suggestions will be useful

Yours

Aj
Newport
Fife

Mon, 07 Nov 2005 22:41:50 GMT
four-parameter logistic equation
Hello AJ,
Not sure what your are asking of Solver. Do you have a set of (x,y) data
that need to be fitted to the stated equation?

Possible worksheet starting in A1

top                    1                 (some starting guesses)
bottom              1
logEc                1
Hillslope            1

x       y          y(calc)
1       23        99
2       34        104
etc

Let the parameters be in B1:B4
Let the X's be in A10:A50, Y's in B10:B50 and Y(Calc) in C10:C50
The y(calc) values come from your formula

In another cell Say B5 enter this formula
DevSq  = SUMXMY2(B10:B50, C10:C50)

Have Solver minimize the value in B5 by varying B1:B4

Now you should have a fairly good agreement between Y and Y(calc)

I would invite you to email me the file but I am off on vacation this
weekend.

Best wishes
Bernard
www.stfx.ca/people/bliengme

Quote:
> Hi

> I am having problems trying to get Excel to do a four-parameter
> logistic equation using the solver add-in.

> y=Bottom + ((Top - Bottom) / (1+ 10(logEC50-X).HillSlope))

> Can anyone tell me if I am asking too much of Excel.

> I have some values got from a curve fitting program (Prism) but when I
> pull them into my equation the curve is no where near the orginal raw
> data.

> Any suggestions will be useful

> Yours

> Aj
> Newport
> Fife

Mon, 07 Nov 2005 23:41:19 GMT

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