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Dec 9, 2015 9:09 AM
(7531 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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Dec 11, 2015 11:06 AM
(10725 views)
| Posted in reply to message from r_o_pedersen0 12/09/2015 08:24 PM

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

6 REPLIES

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Re: 4PL fit (4 parameter logistic)

Dec 9, 2015 9:17 AM
(7032 views)
| Posted in reply to message from r_o_pedersen0 12/09/2015 12:09 PM

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)

Dec 9, 2015 2:10 PM
(7032 views)
| Posted in reply to message from r_o_pedersen0 12/09/2015 12:17 PM

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)

Dec 9, 2015 5:24 PM
(7032 views)
| Posted in reply to message from Jeff_Perkinson 12/09/2015 05:10 PM

Yes it seems everything after the equals sign gets deleted. Thanks for replying. My question concerns the logistic 4P fit in sasjmp. The equation used for this is not the same as for 4 parameter logistic fits used in various applications software I am used to. Is it just not the same model or is there some mathematical point I am missing? Usually 4PL is described as y equals ((A-D)/(1+((x/C)))+D

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Dec 11, 2015 11:06 AM
(10726 views)
| Posted in reply to message from r_o_pedersen0 12/09/2015 08:24 PM

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)

Dec 10, 2015 3:35 AM
(7032 views)
| Posted in reply to message from r_o_pedersen0 12/09/2015 12:09 PM

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)

Dec 11, 2015 4:09 PM
(7032 views)
| Posted in reply to message from r_o_pedersen0 12/09/2015 12:09 PM

Thanks a lot. Those are great answers.