Hi,
1 / [1 + (A * {A/C}^{-t/D})] =
1 / [1 + A^(1-t/D) * C^{t/D}]
with C, D constants so only 1 coefficient...
No problem I guess...
MR
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]
Behalf Of CatharineStacimer
Sent: maandag 5 april 2004 18:02
To: [EMAIL PROTECTED]
Subject: [edstat] Am I solving for one or two coefficients here?
I'm not quite sure how to phrase this possibly basic question: can one
solve a regression equation for two (or more) coefficients if one
coefficient is a function of another? i.e. There is both an intercept
and slope coefficient, but the slope is a function of the intercept.
Specifically, I've been exploring the logistic equation of:
Pt = 1 / (1 + A exp(-Bt))
(A is the timing variable, B is the slope, t is time)
and reading articles using it and working through some examples to
remember the maths and clear out the cobwebs.
Now, one variation of the equation I've seen has B being a function of
A:
B = (1/D * LN {A/C}) where C and D are positive constants
so substituting: this in, Pt
= 1 / [1 + A * exp (-(1/D * LN {A/C}) * t)]
= 1 / [1 + A * exp (-(t/D * LN {A/C})]
and using the fact that for positive N, N^X = e^(X LN(N))
=1 / [1 + (A * {A/C}^{-t/D})]
So are there two coefficients one could solve for here? I'm used to
seeing Y = B1 + B2X2. To me this varation looks somewhat like Y = B1 +
B1X2.
.
.
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