Dear statalisters,
A colleague of mine has asked for help with the following stata query:
Working with non-linear least squares regression, Stata 8 includes a couple of non-linear functions already programmed. The logistic function:
nl log3 Y = b1/(1 + exp(-b2*(X-b3)))
and the Gompertz:
nl gom3 Y = b1*exp(-exp(-b2*(X-b3)))
However, looking at various econometric manuals, these functions are normally of the form:
log Y = b1/(1+(b2*exp(-b3*X)))
gom Y = b1*exp(-b2*exp(-b3*X)))
I can't find a mathematical way to move between the two; are the functions programmed into Stata a recognised alternative form, or is the help file incorrect?
Regards,
Paul
_____________________________________________________________
This e-mail and any attachments may be confidential or legally privileged. If you received this message in error or are not the intended recipient, you should destroy the e-mail message and any attachments or copies, and you are prohibited from retaining, distributing, disclosing or using any information contained herein. Please inform us of the erroneous delivery by return e-mail.
Thank you for your cooperation.
_____________________________________________________________
*
* For searches and help try:
* http://www.stata.com/support/faqs/res/findit.html
* http://www.stata.com/support/statalist/faq
* http://www.ats.ucla.edu/stat/stata/
