Statalist


[Date Prev][Date Next][Thread Prev][Thread Next][Date index][Thread index]

Re: st: How to estimate exponential decay parameter?


From   "Song" <raravise@gmail.com>
To   <statalist@hsphsun2.harvard.edu>
Subject   Re: st: How to estimate exponential decay parameter?
Date   Sun, 23 Mar 2008 15:30:57 -0600

Thank you. That is very helpful.

Reo.

----- Original Message ----- From: "Maarten buis" <maartenbuis@yahoo.co.uk>
To: <statalist@hsphsun2.harvard.edu>
Sent: Sunday, March 23, 2008 1:03 PM
Subject: Re: st: How to estimate exponential decay parameter?



--- Song <raravise@gmail.com> wrote:
My data shows a exponential decay pattern and I want to estimate
exponential decay parameter. How can I estimate 'd' in the following
model using Stata?

Sales(at t) = M*exp(-d*t)

M: initial sales
t: time
d: decay parameter
you can create a new variable ln(Sales) and do a normal regression of
ln(Sales) against t:

ln(Sales) = ln(M*exp(-d*t))
ln(Sales) = ln(M) + ln(exp(-d*t))
ln(Sales) = ln(M) + -d*t

The constant is ln(initial sales)
the effect of t is -d

Hope this helps,
Maarten

-----------------------------------------
Maarten L. Buis
Department of Social Research Methodology
Vrije Universiteit Amsterdam
Boelelaan 1081
1081 HV Amsterdam
The Netherlands

visiting address:
Buitenveldertselaan 3 (Metropolitan), room Z434

+31 20 5986715

http://home.fsw.vu.nl/m.buis/
-----------------------------------------


     __________________________________________________________
Sent from Yahoo! Mail.
More Ways to Keep in Touch. http://uk.docs.yahoo.com/nowyoucan.html
*
*   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/
*
*   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/



© Copyright 1996–2014 StataCorp LP   |   Terms of use   |   Privacy   |   Contact us   |   What's new   |   Site index