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Dec 9, 2015 9:09 AM
(9842 views)

This may be a naïve question but I am confused about the 4PL equation used by jmp in curve fitting. I have a dataset of two variable and I choose: analyze>modeling>nonlinear

Then I plot the data and the red fit-curve button gives the option: Sigmoid curves>logistic curves>Fit logistic 4P

Now my question is; the equation used by jmp is f(x).

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Yes, the parameterization you give is different than the one used in JMP. The following is a reasonable discussion of the two parameterizations. JMP uses the one that it does to avoid having a parameter in an exponent, which makes estimation more difficult.

-Michael

Michael Crotty

Sr Statistical Writer

JMP Development

Sr Statistical Writer

JMP Development

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Re: 4PL fit (4 parameter logistic)

It seems when I posted half my post was deleted??

...now my question is; the equation used by jmp is f(x)

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Re: 4PL fit (4 parameter logistic)

Sorry you had trouble with your post. It seems though that there's still something missing.

Can you clarify your question?

-Jeff

-Jeff

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Re: 4PL fit (4 parameter logistic)

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Yes, the parameterization you give is different than the one used in JMP. The following is a reasonable discussion of the two parameterizations. JMP uses the one that it does to avoid having a parameter in an exponent, which makes estimation more difficult.

-Michael

Michael Crotty

Sr Statistical Writer

JMP Development

Sr Statistical Writer

JMP Development

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Re: 4PL fit (4 parameter logistic)

Hello,

I looked through the Nonlinear Model Library and I found the the 4P logistic model you describe is called the Rodbard Model (4P) in JMP.

Best,

Bill

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Re: 4PL fit (4 parameter logistic)

Thanks a lot. Those are great answers.