Re: Information about S-curve in SPSS

Posted by Sungeun Chung on Feb 09, 2007; 2:44am
URL: http://spssx-discussion.165.s1.nabble.com/Information-about-S-curve-in-SPSS-tp1073784p1073786.html

Edgar,

Thank you for the information.  SPSS has different equations for S-Curve and
Logistics model. The equation for the logistics is the same in Greene
(2000).

Y = 1 / (1/u + (b0 * (b1**t))) or ln(1/y-1/u) = ln (b0) + (ln(b1) * t) where
u is the upper boundary value

The equation of S-curve is  Y = e**(b0 + (b1/t)) or ln(Y) = b0 + (b1/t).

I cannot find the equation for the S-curve in Green (2000).

Any more help?  Thank you.

Sungeun


On 2/8/07, Edgar F. Johns <[hidden email]> wrote:

>
> Take a look at the econometrics literature. The s-curve is also known as
> the
> logistic model or function. A classic example is adoption rate of a new
> product/technology. Initially, the adoption rate is slow until some
> critical
> mass is reached. Then adoption is fast until it reaches saturation.
>
> The classic econometrics text is Greene, W. H. (2000). Econometric
> analysis.
> (4th Ed.). Upper Saddle River, NJ: Prentice-Hall.
>
> Edgar
> ---
> Discover Technologies
> 42020 Koppernick Rd.
> Suite 204
> Canton, MI 48187
> [phone]
> [phone] fax
>
> -----Original Message-----
> From: SPSSX(r) Discussion [mailto:[hidden email]] On Behalf Of
> Sungeun Chung
> Sent: Thursday, February 08, 2007 5:14 PM
> To: [hidden email]
> Subject: Information about S-curve in SPSS
>
> SPSS expert,
>
> I used "Curve Estimation" to find a functional form for my data.  I found
> that S-curve is best fitted.
>
> I found the equation for S-curve in the help menu:
>
> S-curve. Model whose equation is Y = e**(b0 + (b1/t)) or ln(Y) = b0 +
> (b1/t).
>
> I need more information about this function.  Can anyone give me
> references
> about the above equation?
>
> Thanks in advance,
>
> --
> Sungeun Chung, Ph.D.
>
> Assistant Professor
> Department of Communication
> Memorial Hall 303G
> Western Illinois University
> Macomb, IL 61455-1390
> Tel. [phone]
> E-mail: [hidden email]; [hidden email]
>
>

--
Sungeun Chung, Ph.D.

Assistant Professor
Department of Communication
Memorial Hall 303G
Western Illinois University
Macomb, IL 61455-1390
Tel. [phone]
E-mail: [hidden email]; [hidden email]