--- Song <[email protected]> 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/
-----------------------------------------
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