From stoffer at pitt.edu  Tue Apr  4 05:20:43 2006
From: stoffer at pitt.edu (stoffer at pitt.edu)
Date: Tue,  4 Apr 2006 05:20:43 +0200 (CEST)
Subject: [Rd] header containing (PR#8231) -- replace 8231
Message-ID: <20060404032043.B8E3BBDC9@slim.kubism.ku.dk>

Sorry for reporting this again, but I didn't notice that there was a 
response.  The response to PR#8231 is "This is a matter of opinion!"

First, I find this response arrogant and dismissive and I would ask 
for a second opinion. Second, the use of the term "intercept" - 
whether or not you think is "a matter of opinion" - is MISLEADING. Why 
do you want to MISLEAD users?

I believe "intercept-slope form of a line" is well established in 
mathematics.  That is, if y=a+bx then most of us would call a the 
intercept and b the slope.  Is the responder saying this is opinion? 
This is standard terminology.

For a causal AR(1) model we write
X(t) = a + b X(t-1) + W(t)
where W(t) is white noise.  The value a is the intercept and the value 
b is the slope... is the responder saying this is opinion?  How so? 
It's the slope-intercept form of the model.

If mu =E[X(t)] then mu = a + b*mu or
a = mu*(1-b)
is the relationship between the MEAN and the INTERCEPT.  They are not 
the same unless b=0.  This is NOT opinion. This is a fact.

So if I tell you the estimate of the intercept is 10, what does that 
say to you?  In the arima output (and other functions), it's saying 
the estimate of mu is 10.  Really?  You don't think that's misleading?

Again, I put this to you: Why do you want to MISLEAD the user. Get 
some other opinions on this if you don't agree with me.

Thanks again for your time and sorry for the double report.
David

-- 


-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
David S. Stoffer
Department of Statistics
University of Pittsburgh
Pittsburgh, PA  15260

phone: [412] 624-8496
   fax: [412] 648-8814
email: stoffer at pitt.edu
   web: http://www.stat.pitt.edu/stoffer
voice: hey dave



[Rd] header containing (PR#8231) -- replace 8231
stoffer at pitt.edu