Fitting power fnction

[Kornbrot, Diana]

Want to fit following function in spss:
Y = a(X-b)^n
Where Y and X are variables  and a, b, n are parameters to be estimated
Can any one direct me to script to create such a function, hopefully with goodness of fit of model
All help gratefully received
Best

Diana

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Emeritus Professor Diana Kornbrot
email:  d.e.kornbrot@...    
web:    http://dianakornbrot.wordpress.com/
Work
Department of Psychology
School of Life and Medical Sciences
 University of Hertfordshire
 College Lane, Hatfield, Hertfordshire AL10 9AB, UK
   voice:   [phone]
   fax:     [phone]
Home
 19 Elmhurst Avenue
 London N2 0LT, UK
    voice:   [phone]
    mobile: [phone]
    fax:      [phone]

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[David Marso]

NLR, CNLR, maybe Curvefit?
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Kornbrot, Diana wrote

Want to fit following function in spss:
Y = a(X-b)^n
Where Y and X are variables  and a, b, n are parameters to be estimated
Can any one direct me to script to create such a function, hopefully with goodness of fit of model
All help gratefully received
Best

Diana

________________________________
Emeritus Professor Diana Kornbrot
email:  [hidden email]
web:    http://dianakornbrot.wordpress.com/
Work
Department of Psychology
School of Life and Medical Sciences
 University of Hertfordshire
 College Lane, Hatfield, Hertfordshire AL10 9AB, UK
   voice:   [phone]
   fax:     [phone]
Home
 19 Elmhurst Avenue
 London N2 0LT, UK
    voice:   [phone]
    mobile: [phone]
    fax:      [phone]
________________________________

[Jon K Peck]

You can do this with NLR.  Here's an example.
MODEL PROGRAM  a=1000 b=50 n=2.
COMPUTE  PRED_=a*(abs(jobtime-b))**n.
NLR salary  /OUTFILE='D:\spsstemp3\spss3072\SPSSFNLR.TMP'.

But note that I inserted an absolute value function in order to deal with the issue of fractional n with a negative number.


Jon Peck (no "h") aka Kim
Senior Software Engineer, IBM
[hidden email]
new phone: [phone]




From:        "Kornbrot, Diana" <[hidden email]>
To:        [hidden email],
Date:        10/12/2012 12:35 PM
Subject:        [SPSSX-L] Fitting power fnction
Sent by:        "SPSSX(r) Discussion" <[hidden email]>

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Want to fit following function in spss:
Y = a(X-b)^n
Where Y and X are variables  and a, b, n are parameters to be estimated
Can any one direct me to script to create such a function, hopefully with goodness of fit of model
All help gratefully received
Best

Diana

---

Emeritus Professor Diana Kornbrot
email:  d.e.kornbrot@...    
web:    http://dianakornbrot.wordpress.com/
Work
Department of Psychology
School of Life and Medical Sciences
University of Hertfordshire
College Lane, Hatfield, Hertfordshire AL10 9AB, UK
  voice:   [phone]
  fax:     [phone]
Home
19 Elmhurst Avenue
London N2 0LT, UK
   voice:   [phone]
   mobile: [phone]
   fax:      [phone]

---

[Kornbrot, Diana]

Many thanks to Jon Peck and David Marso
Of course, Non Linear Regression [NLR]:  regression > non-linear works absolutely fine, even using dialogue boxes
Parameters are straightforward to defin, with starting points. There are warnings where iterations include neg numbers to fractional powers, but converges fine.
Same solution as R, which is a relief
Was being really stupid & apologize for bothering exellent spss list
Best
Diana


On 12/10/2012 19:53, "Jon K Peck" <peck@...> wrote:

You can do this with NLR.  Here's an example.
MODEL PROGRAM  a=1000 b=50 n=2.
COMPUTE  PRED_=a*(abs(jobtime-b))**n.
NLR salary  /OUTFILE='D:\spsstemp3\spss3072\SPSSFNLR.TMP'.

But note that I inserted an absolute value function in order to deal with the issue of fractional n with a negative number.


Jon Peck (no "h") aka Kim
Senior Software Engineer, IBM
peck@...
new phone: [phone]




From:       "Kornbrot, Diana" <d.e.kornbrot@...>
To:       SPSSX-L@...,
Date:       10/12/2012 12:35 PM
Subject:       [SPSSX-L] Fitting power fnction
Sent by:       "SPSSX(r) Discussion" <SPSSX-L@...>

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Want to fit following function in spss:
Y = a(X-b)^n
Where Y and X are variables  and a, b, n are parameters to be estimated
Can any one direct me to script to create such a function, hopefully with goodness of fit of model
All help gratefully received
Best

Diana

---

Emeritus Professor Diana Kornbrot
email:  d.e.kornbrot@... <d.e.kornbrot@...>    
web:    http://dianakornbrot.wordpress.com/ <http://dianakornbrot.wordpress.com/>
Work
Department of Psychology
School of Life and Medical Sciences
 University of Hertfordshire
 College Lane, Hatfield, Hertfordshire AL10 9AB, UK
   voice:   [phone]
   fax:     [phone]
Home
 19 Elmhurst Avenue
 London N2 0LT, UK
    voice:   [phone]
    mobile: [phone]
    fax:      [phone]

---

---

Emeritus Professor Diana Kornbrot
email:  d.e.kornbrot@...    
web:    http://dianakornbrot.wordpress.com/
Work
Department of Psychology
School of Life and Medical Sciences
 University of Hertfordshire
 College Lane, Hatfield, Hertfordshire AL10 9AB, UK
   voice:   [phone]
   fax:     [phone]
Home
 19 Elmhurst Avenue
 London N2 0LT, UK
    voice:   [phone]
    mobile: [phone]
    fax:      [phone]

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